Russia parliament approves military move in Syria
Russia's upper house of parliament has voted to allow the military to be deployed in Syria, paving the way for air strikes on the militant Islamic State (IS) group.
Within hours of the decision, US officials said Russia appeared to have carried out its first attack.
Senior Kremlin official Sergey Ivanov said no ground troops would be involved in Syria, only the air force.
President Vladimir Putin called this week for a broad anti-terror coalition.
He told the UN it should be similar to the alliance that opposed Adolf Hitler in World War Two.
A US-led coalition has been carrying out air strikes against IS in Syria and Iraq for more than a year.
But Mr Ivanov, the president's chief-of-staff, said US and French air strikes in Syria circumvented international law, since they had not been authorised by a UN resolution or by the Syrian government.
President Bashar al-Assad, he said, had officially requested military assistance from Moscow. That was later confirmed in a statement from the Syrian president's office.
As Russia stepped up its involvement in Syria, reports said Syrian government planes had carried out attacks on three towns north of the city of Homs. At least 17 people were killed, including five children, activists said.
Russia has provided weaponry and military advisers to the Syrian armed forces throughout the war, but satellite images from Syria in recent weeks have revealed a build-up of Russian air power at a base outside the Mediterranean port city of Latakia, the heartland of Mr Assad's minority Alawite sect.
There have been widespread reports of military planes and cargo ships arriving from Russia with supplies. Latest speculation has centred on Russia's most modern fighter bomber, the SU-34 or "Fullback". Unconfirmed reports suggested that six SU-34s had flown into Latakia on Tuesday.
The upper house of parliament, the Federation Council, took a similar vote in March 2014, responding to a request by President Putin to authorise the use of Russian forces in Ukraine, although that was revoked two months later.
Mr Ivanov said that Russia was seeking to target IS because "thousands" of Russian citizens had joined its ranks and would pose a threat upon their return to Russia. Earlier this month a top Russian security official put the number of Russian recruits at 2,400 and at least as many from Central Asia.
"This is not about achieving any foreign-policy goals or satisfying any ambitions, which our Western partners often accuse us of. This is exclusively about Russia's national interests," he said.
Earlier this month, Russia's Human Rights Council said it had been contacted by soldiers who feared they were about to be sent to fight in Syria. But Interfax news agency reported that only officers or professional soldiers would be sent there.
US and Russian leaders have long differed over the Syrian conflict, which has claimed more than 250,000 lives and forced four million people to flee abroad.
The US insists President Assad must leave office, and President Barack Obama told the United Nations General Assembly (UNGA) there could not be a return to the pre-war status quo "after so much bloodshed".
But Mr Putin said it was an "enormous mistake" to refuse to co-operate with the Syrian government against militants.
Some Western leaders have recently softened their stance towards the Syrian president, conceding that he might be able to stay in power during a political transition.
Syria's civil war
What's the human cost?
More than 250,000 Syrians have been killed and one million injured in four and a half years of armed conflict, which began with anti-government protests before escalating into a full-scale civil war.
And the survivors?
More than 11 million others have been forced from their homes, four million of them abroad, as forces loyal to President Assad and those opposed to his rule battle each other - as well as jihadist militants from IS. Growing numbers of refugees are going to Europe.
How has the world reacted?
Regional and world powers have also been drawn into the conflict. Iran and Russia, along with Lebanon's Hezbollah movement, are propping up the Alawite-led government. Turkey, Saudi Arabia and Qatar are backing the Sunni-dominated opposition, along with the US, UK and France.