UNITED NATIONS/BEIRUT - Syria has pledged to withdraw all military units from towns by April 10 to pave the way for a ceasefire with rebels two days later, though Western envoys were skeptical about Damascus' intent to halt its year-long assault on opponents. The UN-Arab League peace envoy Kofi Annan briefed the U.N. Security Council on the deadline behind closed doors. He told them there had been no reduction in violence so far, but urged them to consider an observer mission nevertheless in light of Syria's acceptance of the April 10 deadline, diplomats said. Washington's UN Ambassador Susan Rice, president of the 15-nation Security Council this month, said some council members "expressed concern that the government of Syria not use the next days to intensify the violence and expressed some skepticism about the bona fides of the government in this regard." Syrian President Bashar al-Assad has repeatedly promised to stop his campaign against anti-government activists, which has brought the country to the brink of civil war, but has not kept his word. Annan told the council that the Syrian foreign minister sent him a letter on Sunday saying the government accepted his proposal - the first time the Syrians have accepted a specific deadline. "The Syrians have told us they have put a plan in place for withdrawing their army units from populated zones and surrounding areas. This plan ... will be completed by April 10," Annan's spokesman Ahmad Fawzi said in Geneva. "If we are able to verify this has happened on the 10th, then the clock starts ticking on the cessation of hostilities, by the opposition as well. We expect both sides to cease hostilities within 48 hours," he told Reuters.