Foreign ministers from more than 70 Western and Arab countries are due to meet in Istanbul to explore ways to step up pressure on the Syrian regime and bolster the opposition.
Before the second so-called Friends of Syria meeting, opposition leaders said they now backed calls to arm rebels.
They say President Bashar al-Assad's acceptance of an UN-Arab League peace plan is a ploy to gain time.
The Syrian government, meanwhile, has declared victory over rebel fighters.
Activists say at least 25 people died in violence yesterday, with security forces continuing bombardments in the city of Homs and other areas.
The foreign ministers meeting in Istanbul, who include US Secretary of State Hillary Clinton, are expected to maintain diplomatic pressure on President Assad, largely by insisting that he abide by the peace plan proposed by UN-Arab League envoy Kofi Annan.