ZUHRES, Ukraine — Just hours after the Malaysian government reached an agreement with Ukrainian separatists on Sunday over access to the crash site of a Malaysian airliner shot down in rebel territory, the Ukrainian military launched an operation to recapture the debris fields, again stalling international efforts to secure the site. 
 
 The heavy fighting threatened to torpedo hopes of a breakthrough and cause yet more delays in collecting evidence and retrieving the remaining bodies from the crash. Ukrainian security officials said they needed control over the site to prevent the pro-Russia separatists from destroying clues to the downing of Malaysia Airlines Flight 17. 
 
 By Sunday evening, the Ukrainian advance had blocked a road leading from the provincial capital, Donetsk, to the airplane debris northeast of Shakhtyorsk, but it remained unclear whether government troops were in control of all or part of the approximately 14 square miles of debris fields. 
 
 Videos posted online appeared to show Ukrainian armored vehicles near the site, and reporters who visited earlier Sunday said insurgents were nowhere to be seen. 

 Story highlights Effort to identify bodies will take weeks or months, head of forensics team says 
 
 Rebel leader says Ukraine military breaks through to part of crash site 
 
 Flare-up in fighting near crash site in eastern Ukraine turns back investigation team 
 
 Washington preparing further sanctions against Moscow 
 
 It is, in the words of one frustrated official, "one of the biggest open crime scenes in the world." 
 
 And yet, 11 days after Malaysia Airlines Flight 17 was blown out of the sky by a suspected surface-to-air missile, the Dutch investigators in charge of finding out what happened have yet to lay eyes on the wreckage or the human remains believed to remain strewn across the enormous debris field. 
 
 The latest setback came Monday, when a 45-person team of Dutch and Australian experts, accompanied by monitors from the Organization for Security and Co-operation in Europe, abandoned their effort to reach the site after hearing explosions and being warned of heavy fighting in the area. 
 
 It's the same thing that happened Sunday. 
 
 "We're really sick and tired of being delayed," Organization for Security and Co-operation in Europe spokesman Michael Bociurkiw told CNN's "New Day." 
 
 "We all know there are still human remains out there exposed to the elements, number one," he said. "Secondly, it is one of the biggest open crime scenes in the world as we speak, and it is not secured. There's no security perimeter around the 30- or 35-square-kilometer site." 
 
 16 photos: MH17: What they left behind 16 photos: MH17: What they left behind MH17: What they left behind – A birthday card found in a sunflower field near the crash site of Malaysia Airlines Flight 17 in eastern Ukraine, on Thursday, July 24. The passenger plane was shot down July 17 above Ukraine. All 298 people aboard were killed, and much of what they left behind was scattered in a vast field of debris. Hide Caption 1 of 16 16 photos: MH17: What they left behind MH17: What they left behind – A classical music record is seen among the sunflowers on July 24. Hide Caption 2 of 16 16 photos: MH17: What they left behind MH17: What they left behind – A shoe, appearing to be brand new, sits under foliage at the crash site. Hide Caption 3 of 16 16 photos: MH17: What they left behind MH17: What they left behind – Two Dutch passports belonging to passengers lie in a field at the site of the crash on Tuesday, July 22. Hide Caption 4 of 16 16 photos: MH17: What they left behind MH17: What they left behind – Clothing, sunglasses and chocolate are seen on July 22. Hide Caption 5 of 16 16 photos: MH17: What they left behind MH17: What they left behind – More sunglasses and a travel guide lie in the field on July 22. Hide Caption 6 of 16 16 photos: MH17: What they left behind MH17: What they left behind – A doll is seen on the ground on Saturday, July 19. Hide Caption 7 of 16 16 photos: MH17: What they left behind MH17: What they left behind – A single shoe is seen among the debris and wreckage on July 19. There has been concern that the site has not been sealed off properly and that vital evidence is being tampered with. Hide Caption 8 of 16 16 photos: MH17: What they left behind MH17: What they left behind – Pieces of a wristwatch lie on a plastic cover at the crash site. Hide Caption 9 of 16 16 photos: MH17: What they left behind MH17: What they left behind – A toy monkey. Hide Caption 10 of 16 16 photos: MH17: What they left behind MH17: What they left behind – Books, bags, a tourist T-shirt. Ukraine's government said it had received reports of looting, and it urged relatives to cancel the victims' credit cards. But a CNN crew at the scene July 19 said it did not see any signs of looting. Hide Caption 11 of 16 16 photos: MH17: What they left behind MH17: What they left behind – Passports were scattered across the large field. Hide Caption 12 of 16 16 photos: MH17: What they left behind MH17: What they left behind – Playing cards and euros are seen at the crash site. Hide Caption 13 of 16 16 photos: MH17: What they left behind MH17: What they left behind – A travel guide and toiletries. Hide Caption 14 of 16 16 photos: MH17: What they left behind MH17: What they left behind – Luggage on Friday, July 18. Hide Caption 15 of 16 16 photos: MH17: What they left behind MH17: What they left behind – An empty suitcase is cordoned off near the plane's impact site on Thursday, July 17. Hide Caption 16 of 16 
 
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 According to unconfirmed reports from pro-Russian rebels, Ukraine's military broke through to part of the crash site Monday and had stationed armored personnel carriers and dug trenches there. 
 
 "Safe work of experts and observers is impossible," Vladimir Antyufeev, the acting Prime Minister for the self-proclaimed Donetsk People's Republic, said Monday. 
 
 The United Nations and other countries have repeatedly called for a cease-fire to allow investigators a safe working environment at the crash site, which the U.N. human rights chief said Monday could be the scene of a war crime. 
 
 The Malaysian government had struck a deal with rebels to allow unarmed international police officers to guard the site, but the fighting has made that impossible. 
 
 "This is a contested zone. There is active fighting going on," Andrew Colvin, deputy commissioner of the Australian Federal Police, said at a news conference Monday in Canberra. 
 
 "We are working on the basis that if it's a permissive environment, we will go in," he said. 
 
 Bociurkiw said Monday that investigators will try to reach the site again Tuesday. 
 
 "We will keep trying every day," he said. 
 
 A CNN crew joined the convoy that attempted to go to the crash site Monday, but the media were stopped by armed men near Shakhtorsk. The forensic teams turned around not long later. 
 
 Other people were also fleeing the violence. 
 
 One man said jets were flying over his home. 
 
 "My little one is terrified," the man said. 
 
 Identifying the bodies 
 
 As of Monday, 227 coffins bearing remains from the crashed plane had been sent to the Netherlands, where forensic investigators were working to identify them. 
 
 Of the 298 people killed in the crash, 193 were Dutch, 43 were Malaysian, and 27 were Australian. 
 
 More than 200 forensics experts from all over the world are working at a Dutch military base to identify the remains, according to Howard Day, who is leading the effort. 
 
 Investigators aren't sure how many sets of remains they have. Only one victim -- a Dutch man -- has been identified. 
 
 "This will take weeks; it will take months," Day said. 
 
 Experts are using a variety of approaches in their work, including dental records, DNA analysis and fingerprints, he said. 
 
 "We don't just identify people from a photograph or from an item of property that may be on them, because there's been countless mistakes, examples of mistakes where that's happened in the past over the years, even small incidents, like car crashes," he said. 
 
 Russian role in conflict debated 
 
 The fighting appeared to be moving southeast from Horlivka, a city about 30 miles (about 50 kilometers) northwest of the crash site. At least 13 people, including two children, were killed in fighting Sunday in and near Horlivka, the Donetsk Regional Authority said. 
 
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 At least 332 Ukrainian soldiers have been killed and nearly 1,300 have been injured since April 7, according to Ukraine's National Defense and Security Council and law enforcement agencies. There is no known figure for the number of rebels killed. 
 
 Meanwhile, debate continued over Russia's role in the conflict. 
 
 On Sunday, the State Department released satellite images that it said showed Russians firing into Ukraine. 
 
 "We are putting out evidence to confirm the points that not only has Russia been providing the weapons across the border, including heavy weapons, but they have also now been firing artillery barrages across the border," senior White House adviser Ben Rhodes said. 
 
 Russian officials have denied arming the rebels. At a news conference Monday, Russian Foreign Minister Sergey Lavrov said he hoped that deployment of an Organization for Security and Co-operation in Europe observer mission at two checkpoints on the Russian-Ukrainian border would clarify what was happening on the ground. 
 
 Russia wants 'impartial' MH17 investigation 
 
 U.S. and Ukrainian officials have said that a Russian-made missile system was used to shoot down Flight 17 from rebel territory. Russia and the rebels have disputed the allegations and blamed Ukraine for the crash. 
 
 On Monday, U.N. High Commissioner for Human Rights Navi Pillay said that what happened "may amount to a war crime." 
 
 "It is imperative that a prompt, thorough, effective, independent and impartial investigation be conducted into this event," Pillay said. 
 
 Russia announced over the weekend that it had formed a team to join the investigation, state-run news agency RIA Novosti reported. It will be led by the deputy head of the Federal Air Transport Agency, Oleg Storchevoy. 
 
 Lavrov called for an "impartial" investigation carried out with agreement from the U.N. Security Council. But State Department spokeswoman Jen Psaki said Monday on CNN that the United States has little faith in what Russia says. 
 
 "The Russians have mastered the art of saying one thing and doing another," she said. 
 
 Russian foreign minister shrugs off sanctions 
 
 The United States will place new sanctions on Russia this week, White House Deputy National Security Adviser Tony Blinken announced Monday without elaborating. 
 
 Representatives from EU member states will meet Tuesday to consider the proposals, according to the EU website. 
 
 The new proposals include sanctions on weapons, goods that can be used for both civilian and military purposes, access to European capital markets and on the export of energy technology from Europe to Russia. 
 
 Psaki said Monday that what happens next is up to Russia. 
 
 "We're seeing a serious impact of just the sanctions we have put in place to date," she said. 
 
 "The Europeans want to do more. We expect they'll do more," Psaki said. "So the question for the Russians is, do they care about the economy and how it's impacting their people, or are they just going to be in denial about what impact these sanctions are having?" 
 
 Lavrov said Monday that the Russian government wasn't happy about all the sanctions but that the country would overcome any economic difficulties and become more independent as a result. 
 
 "We are only seeing the desire of our Western partners to punish Russia," he said. 
 
 Also Monday, the United States accused Russia of violating the 1987 Intermediate-Range Nuclear Forces Treaty, citing cruise missile tests that date to 2008, senior State Department and White House officials said. 
 
 "This is a very serious matter which we have attempted to address with Russia for some time now," said a senior State Department official. 
 
 Russia's suspected violation of the treaty was first reported Monday by The New York Times. 
 
 "The 2014 Compliance Report of the treaty includes a determination that the Russian Federation is in violation of its INF Treaty obligations not to possess, produce, or flight-test a ground-launched cruise missile with a range capability of 500 to 5,500 kilometers (310 to 3,417 miles), or to possess or produce launchers of such missiles," a White House official said, adding that they "have kept the Congress and our allies informed of this matter." 
 
 The violation was for cruise missile tests that date back to 2008, prompting an administration review as to whether the tests are in violation of the 1987 treaty between the United States and Russia banning medium range missiles. 
 
 Officials told CNN that Washington had called for senior-level talks, but insisted the situation was not related to the violence in Ukraine. 
 
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 Image copyright AFP Image caption There are fears that some evidence at the crash site may have been compromised as it was not protected 
 
 The downing of the Malaysia Airlines jet in Ukraine may be a "war crime", the UN's human rights chief says. 
 
 Pro-Russia Ukrainian rebels and the Ukrainian authorities have accused each other of shooting down flight MH17. 
 
 A Ukrainian official said on Monday that MH17's data recorders show a "massive explosive decompression" caused by a rocket. 
 
 Meanwhile, heavy fighting has again prevented international police from reaching the crash site. 
 
 Ukraine's military said it was battling separatists for control of several towns near the site in eastern Ukraine. 
 
 All 298 people on board the airliner - mostly Dutch - died on 17 July. 
 
 'War crime' 
 
 International police want to help secure the huge site so that plane wreckage and human remains can be examined by crash experts. 
 
 Most of the bodies have been removed, many of them repatriated to the Netherlands. 
 
 "This violation of international law, given the prevailing circumstances, may amount to a war crime," Navi Pillay, the UN High Commissioner for Human Rights, said of the downing of MH17. 
 
 "Every effort will be made to ensure that anyone committing serious violations of international law including war crimes will be brought to justice, no matter who they are," Ms Pillay said. 
 
 Ms Pillay spoke as the latest UN report on Ukraine suggested at least 1,129 people have been killed and 3,442 wounded in the Ukraine conflict since mid-April. 
 
 Image copyright AP Image caption Ukraine's army says it has advanced into the town of Shakhtarsk, near the crash site 
 
 The conflict has displaced more than 200,000 people, many of whom have fled east to neighbouring Russia. 
 
 Pro-Russian rebels have been accused of attacking the plane with a missile fired from a Buk system, also known to Nato as an SA-11 Gadfly. The missile is designed to explode close to an aircraft, spraying it with shrapnel. 
 
 Flight MH17's two black boxes are currently being analysed by aviation experts in the UK. 
 
 Shelling 
 
 Russian Foreign Minister Sergei Lavrov said he hoped international monitors would be able to deploy on the Ukraine-Russia border in the next few days. 
 
 In a statement on Monday, the Ukrainian military said it had "entered" the towns of Shakhtarsk and Torez and was working to seize control of Pervomaysk and Snizhne - all close to the crash site of MH17. 
 
 A separatist leader in Donetsk, Vladimir Antyufeev, told the AFP news agency that the Ukrainian army had taken over part of the crash site. 
 
 A team of Australian and Dutch police and forensic experts abandoned attempts to reach the site on Monday, blaming the security situation in the area. It was the second failed attempt in as many days. 
 
 Image copyright AP Image caption Fighting prevented a convoy of international forensic experts and police from entering the crash site 
 
 Image copyright EPA Image caption Several civilians were killed in heavy shelling in the city of Horlivka over the weekend 
 
 "We are sick and tired of being interrupted by gunfights despite the fact that we have agreed that there should be a ceasefire," said Alexander Hug, an official from the OSCE mission to Ukraine. 
 
 The army is also trying to take control of two main roads in eastern Ukraine, which the government in Kiev believes to be vital supply lines from Russia for rebel forces in Donetsk. 
 
 In the past 24 hours there has been heavy artillery fire at the city of Horlivka, where several civilians were killed. 
 
 In Donetsk at least three people died in shelling, the municipal authorities say. And there are reports of civilian casualties in the shelling of Luhansk, which is also held by the rebels. 
 
 The US has produced what it calls satellite evidence that rockets have been fired at Ukrainian forces from Russian soil. 
 
 Russia denies that any of its forces are helping the rebels. 

 SHAKHTARSK, Ukraine (AP) — An international police team has failed to reach the crash site of a Malaysian Airlines plane for a second day running as clashes rage in a town on the road to the area. 
 
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 Ukrainian Ministry Emergency officer, left, Donetsk People's Republic fighter, 2nd left, and members of the OSCE mission in Ukraine examine a map as they discuss the situation around the site of the crashed... (Associated Press) 
 
 Dutch, right, and Australian policemen talk in the city of Donetsk, eastern Ukraine Sunday, July 27, 2014. A team of international police officers that had been due to visit the site of the Malaysian... (Associated Press) 
 
 A Donetsk People's Republic APC travels in the city of Donetsk, eastern Ukraine Sunday, July 27, 2014. Ukrainian armed forces mounted a major onslaught against pro-Russian separatist fighters Sunday in... (Associated Press) 
 
 A delegation of Australian and Dutch police and forensic experts stopped Monday in Shakhtarsk, a town around 20 miles (30 kilometers) from the fields where the aircraft was downed. 
 
 Sounds of regular shelling could be heard from Shakhtarsk and residents were fleeing town in cars. 
 
 AP reporters saw a high-rise apartment block in the town being hit by at least two rounds of artillery. 
 
 The mandate of the police team is to secure the currently rebel-controlled area so that comprehensive investigations can begin and any remaining bodies be recovered.
– Heavy fighting has turned back international investigators for a second day from the site where Malaysia Airlines Flight 17 was brought down. The Ukrainian military has launched a major offensive against pro-Russia rebels, and it's no longer clear who's in control of the crash site, reports the New York Times. Dutch and Australian investigators and a forensics team tried to reach the site yesterday and today after an agreement was reached with rebel leaders, but they turned back because of artillery fire, reports the AP. The international team holed up in the town of Shakhtarsk, about 20 miles from the crash site; AP reporters there say they saw an apartment complex struck by artillery fire as residents hightailed it out of town. "This is a contested zone. There is active fighting going on," an Australian police official says, according to CNN. As the Ukraine military battles rebels, there have been reports of casualties in several cities, including Horlivka, around 30 miles from the crash site, where at least 13 people were killed yesterday. UN human rights chief Navi Pillay said today that the downing of the Malaysia jet is a violation of international law that may constitute a war crime and every effort will be made to bring the perpetrators to justice, the BBC reports. The US, meanwhile, has released satellite images it says proves that Russia fired artillery from over the border the week after the jet was downed, reports the AP. Russia denies involvement in the conflict, and its foreign ministry accuses the US of carrying out "an unrelenting campaign of slander against Russia, evermore relying on open lies."