At least three protesters were shot dead by Syrian security forces on Friday on the second day of a nationwide ceasefire meant to restore peaceful political dialogue after 13 months of extreme violence, opposition activists said.The shootings occurred as demonstrators rallied against President Bashar Assad, who has accepted the terms of the United Nations-brokered ceasefire which took effect on Thursday.One person was killed as marchers tried to converge on a central square in the city of Hama. Security forces shot one person dead as worshipers left a mosque in the town of Nawa in the southern Deraa province, where the uprising began.The group said earlier that Forces loyal to Assad fought rebels near the border with Turkey, the first clash since a UN-brokered ceasefire came into effect a day earlier.According to the group, the fighting broke out in the northwestern province of Idlib, close to the border with Turkey, after army troops deployed to try to clear rebels out of the area.Some of the gunmen pulled out when the shooting started, the group's director Rami Abdulrahman said. He said there were no immediate reports of casualties and the fighting appeared to have stopped.The grassroots Local Coordination Committees said there had been heavy gunfire in the village of Kherbet Joz, close to the Turkish frontier. Dozens of tanks were deployed on the edge of the village, it said.Abdulrahman said that Thursday's ceasefire, brokered by international mediator Kofia Annan, appeared to be holding in the rest of the country, but there was still no sign of any army withdrawal from urban centers, as called for by Annan.Meanwhile, French President Nicolas Sarkozy said on Friday that he did not believe Assad's declaration of a ceasefire was sincere and that international observers should be deployed to monitor the situation in the country."I do not believe Bashar Assad is sincere," Sarkozy told news TV channel i>tele in an interview. "Sadly I do not believe this ceasefire."Sarkozy, waging an uphill battle for re-election in a vote that opens on April 22, said he had discussed the issue with US President Barack Obama in a conference call on Thursday."I believe, and I discussed this yesterday afternoon with Barack Obama, that at the very least international observers must be deployed to establish what's going on," he said."I firmly believe the international community should live up to its responsibilities and create the conditions for (setting up) humanitarian corridors," he said.Syrian opposition activists called mass protests for Friday to test a fragile, day-old ceasefire, and international pressure mounted for Damascus to comply fully with a UN-backed peace plan.Sarkozy and Obama called on Syria on Thursday to adhere "scrupulously and without conditions" to a UN-backed plan to end the violence in the country.Syrians took to the streets across the country in small demonstrations after Friday's Muslim prayers, trusting that the two-day-old ceasefire would protect them from the army bullets that have frightened off peaceful protesters for months.Activists said state security forces were out in strength to block streets in many cities to prevent protesters forming major anti-Assad rallies.