Antalya, Turkey - World leaders joined a heavily-guarded summit in Turkey on Sunday to forge a united front against jihadist violence after the Paris gun and bomb assaults but facing stark divisions over conflict-riven Syria.
US President Barack Obama, Vladimir Putin of Russia, China's President Xi Jinping and other leaders gathered at the Mediterranean resort of Antalya two days after the Paris attacks claimed by Islamic State jihadists that killed at least 129 people.
The Paris killings darkened the mood of the summit of the Group of 20 top world economies, with security and the Syrian conflict now eclipsing an economic agenda that will also deal with the spreading refugee crisis, climate change and tax avoidance.
Several sources told AFP that the leaders were working on a rare separate statement to denounce the Paris attacks and terrorism, urged on by host President Recep Tayyip Erdogan who said the summit agenda was now "very different" given the massacre in Paris.
"We need to lead an international fight within a coalition against collective acts of terrorism," Erdogan said on the eve of the summit after meeting with China's Xi, who described terrorism as "a common enemy of humanity".
The gathering, which will take place without French leader Francois Hollande who remains home to lead his shaken country, offers the first possibility of a meeting between Obama and Putin since Russia launched a its own air campaign in Syria.
The West suspects the Russian bombardment is aimed at propping up the regime of President Bashar al-Assad, a difference that risks driving a wedge through the summit, which officially kicks off at midday Sunday (1000 GMT).
The White House has said no formal summit is so far scheduled between the pair, whose icy body language at previous encounters has grabbed as many headlines as their comments.
Erdogan wants to use the summit to cement his status as a global leader after winning a resounding victory in an election last month, held three weeks after a twin suicide bombing in Ankara that killed 102 people and was blamed on Islamic State militants.
But while even Putin and Obama are likely to have no trouble standing together in shared abhorrence of terrorism, overcoming differences on Syria will prove far trickier.
All musical events, including at the official dinner on Sunday night, have been cancelled as a mark of respect for the Paris victims and Turkish state media said the already tight security at the summit was stepped up.
The leaders will probably struggle to find common ground over the Syria crisis, with host Turkey deeply opposed to Russia's air strikes and finding only a lukewarm reaction so far to its proposal for a safe zone free of Islamic State jihadists to be created inside Syria as a haven for refugees.
"I pray and hope that G20 will provide a platform whereby all of these issues can be discussed openly and then we can understand each other," Erdogan said.
Top diplomats gathered in Vienna on Saturday agreed a fixed calendar for Syria that would see a transition government in six months and elections in 18 months but failed to agree on the future of Assad.
Yet officials in Antalya have insisted that they will not allow terrorism to derail the summit.
The refugee crisis is a key topic, with host Turkey housing some 2.2 million Syrian refugees from the conflict but the European Union wanting Ankara to do more to prevent migrants undertaking risky boat crossings to the EU.
Discussions on climate change will assume greater importance than usual coming just ahead of a UN conference in Paris that aims to agree a legally binding global climate treaty.
Other key guests at the summit include Saudi King Salman, whose delegation according to the Hurriyet daily has booked 546 hotel rooms at a cost of up to 15,000 euros (US$16,115) each and hired 400 luxury cars.