US president Barack Obama has vowed to step up efforts to eliminate Islamic State in Syria and prevent it from carrying out attacks like those in Paris, while European leaders urged Russia to focus its military efforts on the radical Islamists.

Speaking at a G20 leaders summit in Turkey, Mr Obama described the killings in Paris claimed by Islamic State as an attack on the civilised world and said the United States would work with France to hunt down those responsible.

The two-day summit brings Mr Obama and fellow world leaders just 500 kilometres from Syria, where a four-and-a-half-year conflict has transformed the Islamic State group (IS) into a global security threat, and spawned Europe’s largest migration flows since World War II.

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“The skies have been darkened by the horrific attacks that took place in Paris just a day and a half ago,” Mr Obama said after meeting Turkish president Tayyip Erdogan.

“We will redouble our efforts, working with other members of the coalition, to bring about a peaceful transition in Syria and to eliminate Daesh as a force that can create so much pain and suffering for people in Paris, in Ankara, and in other parts of the globe,” he said, using an alternative name for IS.

Turkey’s president Tayyip Erdogan and US president Barack Obama attend a working session at the G20 summit. Photo: ABC

Mr Obama and his Western allies now face the question of how the West should respond after IS again demonstrated it posed a threat far beyond its strongholds in Syria and Iraq.

Washington already expects France to retaliate by taking on a larger role in the US-led coalition’s bombing campaign.

“We’re confident that in the coming days and weeks, working with the French, we will be able intensify our strikes against ISIL in both Syria and Iraq to make clear there is no safe haven for these terrorists,” US deputy national security adviser Ben Rhodes said in an interview with NBC’s Meet the Press.

But European Council president Donald Tusk said Russia too should focus its military operations on IS, rather than on the Syrian opposition battling president Bashar al-Assad, urging cooperation between Washington and Moscow.

“It should be our common aim to coordinate our actions against Daesh and for sure the cooperation between the United States and Russia is a crucial one,” he said.

Obama-Putin side meeting

Russia joined the conflict a month-and-a-half ago with air strikes in Syria, but has been targeting mainly areas where foreign-backed fighters are battling Assad, its ally, rather than Islamic State, its critics say.

French police released this image of Paris terror suspect Abdeslam Salah. Photo: ABC

Turkey and Western allies, by contrast, want Mr Assad out.

UN secretary-general Ban Ki-moon said he welcomed the renewed sense of urgency to find a solution to the war in Syria after the Paris attacks, adding the world had a “rare moment” of diplomatic opportunity to end the violence.

Mr Obama and Russian president Vladimir Putin held an informal discussion at the G20 meet, huddling together on the sidelines of a working lunch.

It was not known what they talked about as they spoke for more than 30 minutes.

Mr Obama is also seeking to coax other European and Middle Eastern countries into more tangible steps to show their military commitment and was expected to hold a bilateral meeting with Saudi Arabia’s King Salman.

In a call last month, the two leaders affirmed the need to cooperate against IS.

Mr Obama said he had also discussed in his meeting with Mr Erdogan the progress made by foreign ministers in Vienna, who on Saturday outlined a plan for a political process in Syria leading to elections within two years, although differences over Mr Assad’s fate still remained.