UN peace envoy Kofi Annan has said there is international agreement that a transitional government should be set up in Syria.
This could include both members of the government and opposition, he said after talks in Geneva.
But US Secretary of State Hillary Clinton said Syrian President Bashar al-Assad could not remain in power.
Meanwhile, activists said a funeral procession in a suburb of Damascus came under mortar attack and 30 people died.
The UK-based Syrian Observatory for Human Rights released amateur video footage claiming to show the explosion in Zamalka, a town 10km east of the Syrian capital.
There has been no independent confirmation of the incident.