France says it will push for a UN resolution, which could ultimately involve military force, if the violence in Syria continues.
On Wednesday, amateur video emerged purporting to show the aftermath of an attack by security forces on a bus in the northern province of Idlib.
Four civilians were reportedly shot dead.
“Either this mediation is working or it isn’t,” Alain Juppe, French Foreign Minister, said.
“If it doesn’t work, we cannot continue to allow ourselves to be challenged by the regime in place, which has not adhered to the six points of the Kofi Annan plan. We’d have to move into a new phase.”
Juppe has also demanded that 300 authorised UN observers be deployed to Syria within 15 days.
Syria has reportedly said that it will bar access to any staff from countries in the “Friends of Syria” group.