Putin said the action was pre-emptive, warning that Moscow would be hunting down Islamic State militants before they target Russia.
"The only correct way to fight international terrorism... is to act preemptively, to battle and destroy fighters and terrorists on the territories they have already seized, not to wait for them to come to us," Putin said.
The Russian defence ministry said Moscow had launched targeted air raids against the 'terrorists' in Syria. A Syrian security source said the war planes hit three provinces.
The strikes came as Putin and US President Barack Obama push rival plans on ways to defeat the Islamic State group in Syria and on the future role of the country's embattled leader Bashar al-Assad.
"They gave us a heads-up they were going to start striking in Syria," a US defence official said. "It was in the vicinity of Homs."


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