US President Barack Obama at the G20
US President Barack Obama at the G20 summit in TurkeyGetty Images

US President Barack Obama vowed to renew efforts to defeat Islamic State in the wake of the terror attacks in Paris in which 129 people were killed. "The skies are darkened by the horrific attacks that took place in Paris," he told reporters at the G20 summit in Turkey.

Obama said that talks at the two-day meeting of the world's richest 20 nations would focus on how to defeat the terrorist group. "The killing of innocent people based on a twisted ideology is an attack not just on France, not just on Turkey, it is an attack on the civilised world," Obama said after a meeting with Turkish President Recep Tayyip Erdoğan.

"The skies are darkened by the horrific attacks that took place in Paris. We stand in solidity with (the French people) in hunting down the perpetrators of this crime and bringing them to justice," Obama said.

Obama said that among the topics he discussed with President Erdoğan were ways to strengthen Turkey's border with Syria, where Isis controls swaths of territory, strategy for dealing with the refugee crisis, and ways to bring about a negotiated end to the conflict.

"We will redouble our efforts, working with other members of the coalition, to bring about a peaceful transition in Syria and to eliminate (ISIS) as a force that can create so much pain and suffering for people in Paris," Obama said.

As French authorities deal with the fallout from the attacks, French President Francois Hollande cancelled plans to appear at the summit, with his place taken by French foreign minister Laurent Fabius.

In talks on the sideline of the summit, Obama and Russian president Vladimir Putin agreed that UN-backed peace talks were necessary to bring to an end the four-and-a-half year conflict in Syria, in which Isis has seized more than 50 per cent of the country's territory.