France denounced as "unacceptable" a Syrian demand for guarantees from armed rebels before it would pull back its troops from protest hubs, in a strongly worded foreign ministry statement Sunday.

"France forcefully condemns the continuing massacres perpetrated by the Syrian regime," said the statement issued by ministry spokesman Bernard Valero.

The Syrian foreign ministry's request came as a weekend escalation in violence claimed almost 180 lives, most of them civilians, ahead of a UN deadline of Tuesday for regime forces to cease fire.

But the French ministry statement said Syrian President Bashar al-Assad had already accepted the terms of international envoy Kofi Annan's peace plan.

"While the regime of Bashar al-Assad announced that it accepted the Annan plan and itself proposed the date of April 10 for the withdrawal of its troops and its heavy weapons from urban centres, he is now making unacceptable new demands," it added.

The surge in bloodshed prompted harsh words on Sunday from Annan, who said the escalation was "unacceptable".

The French ministry statement said that it too was "shocked at the atrocities that continue to be committed in Syria".

Paris pledged its continuing support for and confidence in Annan, the statement added.