ANTALYA, Turkey (AFP) - World leaders on Monday took a first, cautious step towards uniting over how to stop the bloodshed in Syria and smash the ISIS (Islamic State in Iraq and Syria) network at the global G20 summit held in the shadow of the Paris attacks.

US President Barack Obama hailed the move an unprecedented opportunity to end the four-year war in Syria and destroy the extremist "face of evil".

"What is different this time, and gives us some degree of hope, is that for the first time all major countries on all sides of the Syrian conflict agree on a process to end this war," he said after the two-day summit in the Mediterranean resort of Antalya in Turkey.

ISIS leaders "will have no safe haven anywhere", he added at the annual gathering of leaders from Group of 20 top world economies, vowing a ruthless pursuit of the group but without putting US troops on the ground.

French President Francois Hollande stayed home to lead his shaken nation, replaced at the summit by Foreign Minister Laurent Fabius. In Paris, Hollande said he planned to meet with Obama and Putin in the coming days to create a broad anti-ISIS coalition.

At the G20 summit, leaders described the massacre in Paris as an "unacceptable affront to all humanity", according to a rare separate statement accompanying a final communique.

Concretely, they will share intelligence to crack down on the movement of foreign fighters across borders, the statement said.

They also urged "all states" to share the financial burden of coping with refugees, with hundreds of thousands pouring out of war-torn Syria to take the often dangerous path to Europe.

British Prime Minister David Cameron also joined Germany in calling a UN-backed donors conference for February in London to help pay the soaring costs of the refugee crisis.

Western leaders sought in particular to narrow important differences with Russian President Vladimir Putin on resolving the conflict in Syria.

"I think that not only we are able, but it is also indispensible" to form a coalition to fight ISIS extremists, Putin told reporters after the summit.

Moscow stepped up its involvement in Syria in September by launching a bombing campaign of its own that has been welcomed by the regime but greeted with suspicion in the West.

Cameron said the split between the West and Russia on Syria narrowed during talks between foreign ministers in Vienna this weekend but more work needed to be done to unify positions.

"There is still a very big gap but I think there is still some hope that this process could move faster in the future than it has in the past," he said after meeting Putin.

But he lamented how the "body count had piled up in Syria" despite a multitude of summit meetings since the start of the war.

"The faster we can degrade and destroy (ISIS) the safer we will be," Cameron said.

Russia has refused to abandon its support for Syrian President Bashar al-Assad in the four-year civil war, which has claimed more than a quarter of a million lives and displaced millions of people.

A real thaw in the split over Syria emerged on Sunday as Obama held one of his most intimate discussions yet with Putin. Both men were captured by TV cameras as they hunched over a coffee table in animated, impromptu talks on the sidelines of the summit.

US officials said the two leaders agreed on the need for a political transition for Syria that would be set up by a ceasefire and UN-brokered talks.

The Kremlin said the two sides shared the same goal of fighting ISIS but differed on tactics. World powers remain notably divided over what should happen to Assad, who has been backed by Moscow.

G20 host Turkish President Recep Tayyip Erdogan on Monday said the Syrian leader had "no place" in the country's future.

In the special statement at the end of the G20 gathering, world leaders vowed to share intelligence, track border crossings and boost aviation security to halt the movement of jihadist fighters.

German Chancellor Angela Merkel called for "intensive cooperation" between intelligence agencies as well as the military in the fight against terror. Obama revealed here that US agencies will specifically boost such exchanges with France.

Despite the heavy shadow cast by the attacks in Paris, world leaders pressed on with their original agenda, pledging in a draft to agree legally-binding goals on climate change at a conference in Paris from Nov 30-Dec11.

The G20 summit next year moves to China, followed by Germany in 2017.