Multiple attacks in Paris claimed by Islamic State jihadists increased the pressure on some 20 countries and organisations meeting in Vienna on Saturday to overcome deep divisions and help end Syria's civil war.
Witnesses said that the gunmen who killed almost 130 people in Friday's wave of attacks shouted "Allahu akbar" ("God is greatest") and blamed French military action in Syria against Islamic State (IS) extremists.
Vowing no stop to French "international action", Foreign Minister Laurent Fabius said in Vienna that the killings underlined the need to "increase the international coordination in the struggle against Daesh (IS)."
Russian Foreign Minister Sergei Lavrov agreed, saying that the attacks were "no justification" to ease up on tackling radical jihadists such as IS and the Al-Nusra Front, affiliated to Al-Qaeda.
And US Secretary of State John Kerry said that the attacks will "stiffen our resolve, all of us, to fight back."
"If they’ve done anything they’ve encouraged us today to do even harder work to make progress and to help resolve the crises that we face," he said.
EU foreign policy chief Federica Mogherini said that the bloodbath added "another kind of meaning" to the gathering.
"The countries sitting around the table have almost all experienced the same pain, the same terror," she said, citing the recent Russian plane disaster in Egypt and suicide bombings in Beirut and Turkey.
- 250,000 dead -
In almost five years, fighting between the regime of Syrian President Bashar al-Assad and rebel groups as well as IS militants has killed over 250,000 people and forced millions into exile, leaving many of them stranded in neighbouring states.
Others have headed to Europe, causing major splits in the European Union over how to stem the flow and share out the new arrivals among the bloc.
At the last Syria talks on October 30, the participants -- who include Iran and Saudi Arabia -- urged the UN to broker a peace deal between the regime and opposition to clear the way for a new constitution and elections.
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Building on that, this round of talks will try to agree on a roadmap for peace that would include a ceasefire between Assad's forces and some opposition groups, diplomats say.
But a key issue -- which was absent from the last meeting's declaration -- remains Assad's future.
Western and Arab countries want him out of the way in order to allow a transitional government to unite the country behind a reconciliation process and to defeat IS.
British Foreign Secretary Philip Hammond said on Friday that Assad "has to go".
He added, however, that Western powers "recognise that if there will be a transition he may play a part, up to a point, in that transition".
But Russia, carrying out air strikes against Syrian rebels since late September, is together with Iran sticking by Assad.
"Syria is a sovereign country, Bashar al-Assad is a president elected by the people," Russian President Vladimir Putin said in an interview released Friday.
- 'Walls of mistrust' -
Putting that aside, the talks will focus on deciding which of the Syrian government, rebel and opposition factions -- none of whom will be represented at the talks -- will shape the country's future.
But deciding which of the many opposition groups are moderate enough to be acceptable and which to sideline as "terrorists" is likely to be no easy task.
"I cannot say... that we are on the threshold of a comprehensive agreement, no," Kerry had said on Thursday.
"The walls of mistrust within Syria, within the region, within the international community are thick and they are high."