Representatives from more than 100 countries are holding talks in Paris in a fresh attempt to decide what should be done to end the violence in Syria.
Opening the Friends of Syria group meeting, French President Francois Hollande said Syria’s crisis was now a threat to world peace and security.
However, Russia and China – two of Syrian President Bashar al-Assad’s most important allies – are not attending.
On Thursday it emerged a senior member of Syria’s regime had gone to Turkey.
The pro-government website Syriasteps said Brig Gen Manaf Tlas had made an “escape” but that this was “insignificant”.
Sources confirmed his departure to the BBC. But it is not clear whether he has defected.
It would be the highest-level defection of a supporter of President Assad since the rebellion against him started 16 months ago.
Earlier rumors about his possible defection in March proved to be false.
Brig Gen Tlas, of the Republican Guard, is the son of a former Syrian defense minister. As a young man he attended military training with Assad.
The Paris meeting follows similar events in Tunis and Istanbul which demanded tougher action against the Assad regime.
The US and its Western allies are expected to encourage Gulf states to do more to push for global sanctions.
But Russia and China, which both hold vetoes in the United Nations Security Council, are not at the meeting.
Opening the meeting, French President Francois Hollande said it was a “human and political necessity” to stop the conflict
“The crisis has become a threat to international peace and security,” he said, “and we have to draw the conclusions.”
The description refers to Chapter 7 of the UN charter, which allows for the possibility of the use of military force.
UN diplomats are working on a document calling for restrictions on commercial activity if Assad fails to abide by UN and Arab League envoy Kofi Annan’s ceasefire plan and roadmap for a political transition.
The roadmap – announced last weekend by Annan after a meeting of world powers in Geneva – includes an interim government to enable the Syrian people to live ”independently and democratically”.
The Western powers believe that Assad should play no part in Syria’s future, but the roadmap allows Assad an effective veto over any interim candidate he opposes, according to BBC.
Some 15,800 people have died in more than a year of violence in Syria, activists say.
