Russia launched its first air strikes in Syria on Wednesday after President Vladimir Putin won parliamentary permission to use force abroad, the United States said.

A US official said the strike was near the city of Homs in what is Moscow's first engagement in a distant theatre of war since the Soviet occupation of Afghanistan.

Russia's deepening engagement in Syria comes 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."

The Russian defence ministry declined to immediately confirm the strikes.

President Vladimir Putin had just hours earlier won permission from the upper house of parliament, the Federation Council, to deploy troops abroad.

"The Federation Council unanimously supported the president's request," the Kremlin's chief of staff Sergei Ivanov said.

He said the decision to launch air strikes was taken after Assad asked Russia for military support.

Ivanov, a former defence minister, declined to give details of the operation, saying only it would be limited in duration and ruling out ground operations by Russian troops.

Damascus confirmed Assad had requested military assistance from Russia.

Putin is seeking to muscle his way back onto the world stage after months of Western isolation following Russia's seizure of Crimea from Ukraine and support for a separatist insurgency in the east of the ex-Soviet country.

Differences with the West

Russia is later Wednesday to preside over a special UN Security Council meeting on countering terrorist threats that is bound to produce a sharp difference of views between Moscow and Washington.

Addressing the UN General Assembly for the first time in a decade, Putin on Monday proposed a broad UN-backed coalition to fight IS militants and clashed with Obama on the future of Assad.

Washington and its allies blame Assad for the mayhem in Syria, where four years of bloodshed have killed more than 240,000 people.

France meanwhile said it has launched a probe into Assad's regime for alleged crimes against humanity, saying it was forced to act in the face of "systematic cruelty".

The French investigation is largely based on evidence from a former Syrian army photographer known by the codename "Caesar," who defected and fled the country in 2013, bringing with him some 55,000 graphic photographs.

France, which is part of the US-led coalition against IS, carried out its first air strikes against the extremists' positions in Syria on Sunday.

The Syrian Observatory for Human Rights monitoring group said the bombs killed at least 30 jihadists, including 12 child soldiers.

Russia argues that the West should support Assad in his fight against the jihadists.

But Washington says the Syrian leader must go if the Islamic State group is to be defeated.

National interests, not ambitions

The Pentagon says Russia has in recent weeks sent warplanes and other military hardware to northwestern Syria -- along with at least 500 troops -- in what many fear is an attempt to keep the war-torn country's president in power.

Moscow's proposal has exposed differences among Washington's European allies, with some siding with Obama and others saying Moscow should have a greater role in fighting Islamic State.

Russia's military involvement in Syria will be Moscow's first engagement outside the former Soviet Union since the occupation of Afghanistan in 1979.

Putin had also sought permission from the council to deploy military forces in Ukraine ahead of Russia's annexation of Crimea from Ukraine in March 2014.

Konstantin Kosachev, head of the council's international affairs committee, said Russia's forces would be working in close coordination with Syria's army and stressed Moscow would not be sucked into a protracted conflict.

Ivanov said that by moving to launch air strikes in Syria, Russia was acting in the national interest, to prevent foreign terrorist fighters from crossing its borders.

"We are not talking about achieving some foreign policy goals, satisfying someone's ambitions -- what our Western partners regularly accuse us of."

'Hide your sons'

But many analysts accused the Kremlin of a short-sighted approach.

Alexander Konovalov, head of the Strategic Analysis Institute, said Russia was guided by a desire to end its diplomatic isolation and may not fully realise long-term consequences of a military involvement in Syria.

"We were coming to Afghanistan for six months and stayed there for 10 years," he told AFP, referring to a conflict that killed over 14,000 Soviet troops between 1979 and 1989.

According to a recent poll by the respected Levada Centre, 69 percent of Russians are against Moscow's deployment of troops in Syria, with just 14 percent in favour.

Wednesday's news set social networks alight, with many commentators predicting dire consequences for Russians.

"Hide your sons," one Russian, Zaira Abdullaeva, wrote on Facebook.