French President Francois Hollande on Wednesday called for a new Syria peace conference as part of efforts to end a conflict which has claimed some 250,000 lives and destabilised the whole region.

"I call for a new peace conference so that all the countries who want to see peace restored in Syria can contribute," Hollande said.

"All those who can contribute... should get around the table," he said as he went into an emergency EU leaders' summit in Brussels on how to deal with an influx of refugees, many of them fleeing the war in Syria.

Two Geneva peace conferences held under UN auspices in 2012 and 2014 broke down in acrimony when a divided opposition and their Western backers balked at any role for President Bashar al-Assad in the country's future.

Washington and its allies including France insisted Assad had to go.

But Russia backed and continues to back Assad as a bulwark against what it sees as a terrorist threat worsened by Western bungling.

After a string of reverses for Assad on the ground, Moscow has begun supplying him with fresh military supplies and reinforced facilities in the president's Western fiefdom.

The Russian build-up has caused serious concern in Washington but some argue Moscow might prove an important partner in a joint fight against Islamic State jihadis who have seized large swathes of Syrian territory.

Hollande recently ordered French reconnaissance flights over Syria to prepare for possible attacks against IS and he said he was in close contact with Britain which is considering but has not decided on such action.

"Yesterday I was in London with (Prime Minster) David Cameron. As concerns Syria, we have further reinforced our cooperation, our exchanges of information and I am waiting for Britain to take decisions concerning Syria," he said.

"But we will without doubt have to increase our pressure, the reconnaissance flights that we are carrying out, then if we have targets, objectives, that will be translated into airstrikes."