Russia says it has started to bomb Islamic State targets in Syria.
The Russian defence ministry said a number of airstrikes had targeted vehicles and warehouses belonging to miiltants.
The apparent strikes come just hours after Vladimir Putin was given permission to use military force in Syria by his country’s parliament.
Russia has been building up its military presence in Syria, where it supports the government forces of President Bashar al Assad.
There are currently 32 Russian warplanes based near the Syrian port city of Latakia, guarded by 1,700 Russian marines.
It is unclear whether Russia intends to target all forces opposing al Assad – including US-backed rebels – or just extremists, such as IS.
Speaking about the military action, Mr Putin said the only way to deal with terrorists was to do so preemptively.
He said that if terrorists succeeded in Syria, they would then come to Russia – and that must not happen.
Sergei Ivanov, head of the Kremlin administration, said permission to use military force did not mean that ground forces would be engaged.
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He said the move referred to the use of the air force only.
A US defence official said that Russian military jets have already started carrying out air strikes in Syria, near Homs.
But American officials do not believe those attacks are targeting IS, raising concerns over exactly who Mr Putin has in his sights.
Syria confirmed it had written to Russia to request support.
Sky’s diplomatic editor Dominic Waghorn said: “Putin’s been flying drones over parts of Syria, not where Islamic State are based, but where there are rebel groups, some of whom are close to, and are backed by America.
“So is he going to target all of Assad’s enemies, or is it just going to be Islamic State?
“If it is Islamic State, he’s not been gathering intelligence on them, here.”
The last time the Russian parliament granted Mr Putin the right to deploy troops abroad, Moscow seized Crimea from Ukraine last year.
Russia’s move comes as the first French airstrikes in Syria earlier this week killed 30 IS militants at a training camp.
President Francois Hollande said six French jet fighters destroyed the camp in a five-hour operation.
The casualties – including several teenage fighters from Arab countries – were confirmed by the UK-based Syrian Observatory for Human Rights.
Elsewhere, a coalition led by the United States conducted four air strikes on IS in Syria.
The strikes were spread among Deir ez-Zor, Washiya and Palmyra, where they destroyed excavators belonging to the militant group.
France has also confirmed it is now investigating Mr al Assad over alleged crimes against humanity.
The investigation is further examining claims of torture and kidnapping by Mr al Assad’s forces.
It was opened “on the basis of indications received from the foreign ministry” on 10 September, an official at the prosecutor’s office said.
An estimated 250,000 people have been killed in Syria’s four-year civil war between Mr al Assad’s troops, rebel groups and Islamic State.
A further 11 million have been displaced.