Ukraine's Poroshenko vows response to Luhansk plane downing
Ukraine's President Petro Poroshenko has vowed to retaliate after pro-Russia separatists shot down a military plane in the east, killing 49 people.
Those involved in such "cynical acts of terrorism" must be punished, said Mr Poroshenko, who summoned security officials for an emergency meeting.
The defence ministry said the Ilyushin-76 transport plane came under anti-aircraft fire over the city of Luhansk.
It was about to land there, carrying troops and military equipment.
It is thought to be the biggest loss of life suffered by government forces in a single incident since the Ukrainian government in Kiev began an operation to try to defeat the insurgency in the east.
Separately, Moscow has reacted angrily to a violent protest outside its embassy in Kiev, which saw windows smashed and the Russian flag torn down.
Russia's foreign ministry accused Ukrainian police of doing nothing to halt the attack, saying it was a "grave violation of Ukraine's international obligations", and demanded Kiev take steps to ensure the safety of its diplomats.
Ukrainian defence ministry officials are investigating how the separatists brought down the plane in the east, with reports suggesting the use of three "Stinger-like" missiles or a large-calibre machine-gun.
Everyone on board - nine flight crew and 40 troops - was killed.
In a statement released later on Saturday, Mr Poroshenko said: "Ukraine needs peace. However, the terrorists will receive an adequate response."
Rebel fighters were seen combing through the charred wreckage of the plane, south-east of Luhansk, on Saturday.
"This is how we work," one of them, who identified himself as Pyotr, told Reuters news agency. "The fascists can bring as many reinforcements as they want but we will do this every time."
The eastern regions of Donetsk and Luhansk declared independence last month. In March Russia annexed the Crimean peninsula in the wake of the removal of Ukraine's pro-Moscow President Viktor Yanukovych.
Analysis: Jonathan Marcus, BBC diplomatic correspondent
Now Nato has released satellite imagery, linked to existing video material, which appears to give added weight to assertions from the Ukrainian authorities that the tanks used by separatist forces that crossed into its country just a few days ago were indeed supplied by the Russians.
The evidence shown comes from Nato military sources and is not necessarily conclusive. But, despite Russian denials, it is strongly suggestive of the narrative that Nato is setting out.
It should be noted that Russian spokesmen have denied a number of things in regard to operations in Ukraine which have turned out to be untrue.
The incident came less than a week after pro-Russia rebels launched a series of attacks on Ukrainian forces at Luhansk International Airport.
The airport has been under the control of government forces but the rebels hold most of the rest of the city.
Luhansk is the main city of one of two eastern regions where pro-Russia separatists have declared independence from Kiev.
The "anti-terrorist operation" by Ukrainian government forces has left at least 270 people dead over the past two months.
Mr Poroshenko had said that fighting must end "this week" following his inauguration last Sunday.
Meanwhile Nato has released satellite pictures which it says "raise significant questions'' about Russia's role in eastern Ukraine.
The alliance said the images showed Russian tanks recently arrived at a staging area near the border. Ukrainian officials have said the tanks later rolled into Ukraine.
The separatists have argued that tanks spotted in the region belong to the government. But Nato said they bore no army markings, "which is reminiscent of tactics used by Russian elements that were involved in destabilising Crimea".
The US on Friday said it was confident that tanks being used by separatists in eastern Ukraine came from Russia.
"No Ukrainian tank units have been operating in that area," a US state department spokeswoman said.
Russia has denied allegations that it is giving military support to the rebels.
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