PARIS France called on Friday for the creation of aid corridors to help Syrians escape "massacres", saying a U.N.-brokered ceasefire offered an opportunity to put the humanitarian measures in place.
Three anti-government protesters were killed when forces loyal to Bashar al-Assad fought rebels near the border with Turkey, undermining the day-old truce negotiated by peace envoy Kofi Annan.
"I firmly believe the international community should live up to its responsibilities and create the conditions for humanitarian corridors so that these poor people who are being massacred can escape a dictator," President Nicolas Sarkozy told news TV channel i>tele.
Expressing doubt about Assad's commitment to the truce, Sarkozy added: "I do not believe Bashar al-Assad is sincere. Sadly I do not believe this ceasefire," he said.
Sarkozy, waging an uphill battle for re-election in a vote that opens on April 22, said he discussed Syria with U.S. President Barack Obama on Thursday, including a U.N.-backed plan to send observers to ensure it was being implemented.
The Security Council is set to vote on the observer mission later on Friday.
Paris, which has led calls for Assad to step aside, wants a safe passage for relief organisations - with Syrian approval or an international mandate - to get food and medicine to civilians caught up in the fighting.
Annan's spokesman in Geneva also called for aid corridors to be opened, saying about 1 million people needed help in Syria.
Under the French plan to bring in aid, humanitarian corridors would link the frontiers of Turkey, Lebanon or Jordan, to the Mediterranean coast or to an airport.
Foreign Minister Alain Juppe has said the zone could be protected by armed "observers", but has ruled out direct military intervention. Diplomatic sources say a U.N. resolution would be needed to create the corridors, but who would protect it, be it peacekeepers or unarmed observers, is unclear.
Juppe's spokesman Bernard Valero said there was no specific plan, but that with a ceasefire in place, setting up corridors could be easier, unlike previous efforts which failed after Syria, Russia and China opposed them.
"There is a humanitarian urgency," Valero said. "We're in a different situation now to when Assad's helicopters and tanks were firing on everything that moved. The ceasefire opens up new opportunities for humanitarian aid."
Syrian opposition activists called mass protests for Friday to test the fragile, day-old ceasefire.
Juppe said the Assad government had agreed to allow peaceful demonstrations as part of Annan's six-point plan to end the violence and begin political dialogue.
"The demonstrations must be allowed to take place today and if the regime were to crack down on them, it would be a clear violation of its commitments," Juppe said.
Sarkozy and Obama said they would continue to apply pressure on Damascus, including at the U.N. Security Council.
As part of those efforts, Paris will hold an April 17 meeting of about 50 countries, including European Union and Arab League states, to discuss strengthening sanctions and ensuring that existing ones are implemented.
Valero also said Paris had now gathered information and witness accounts of crimes against humanity committed by Assad's government and was working to establish who exactly was responsible.
"The atrocities committed in Syria for more than a year can not be left unpunished," Valero said.
(Additional reporting by Brian Love; Editing by Giles Elgood and Geert De Clercq)