UNITED NATIONS - Syria has not fully complied with its obligations to withdraw troops and heavy weapons from towns and has yet to send a "clear signal" about its commitment to peace, the UN chief told the Security Council in a letter obtained by Reuters on Wednesday.UN Secretary-General Ban Ki-moon said an expanded UN monitoring mission for Syria would comprise "an initial deployment" of up to 300 unarmed observers who would supervise a fragile week-old ceasefire between forces loyal to President Bashar Assad and opposition fighters seeking to oust him."The Syrian Government has yet to fully implement its initial obligations regarding the actions and deployments of its troops, or to return them to barracks," he told the council."Violent incidents and reports of casualties have escalated again in recent days, with reports of shelling of civilian areas and abuses by Government forces," he said. "The Government reports violent actions by armed groups.""The cessation of armed violence is therefore clearly incomplete," Ban said, adding that both sides say they are committed to ending the "violence in all its forms."Diplomats on the 15-nation council say Ban's report and a briefing they will receive from UN-Arab League mediator Kofi Annan's deputy Jean-Marie Guehenno on Thursday at 9:00 a.m. EDT (1300 GMT) will be crucial in determining whether the conditions are right for deploying a UN monitoring mission to Syria.Ban said such a force would be helpful in securing an end to all fighting though it was essential the conditions be right for deployment."Developments since 12 April underline the importance of sending a clear message to the authorities that a cessation of armed violence must be respected in full, and that action is needed on all aspects of (Annan's) six-point (peace) plan," he said."At the same time the very fragility of the situation underscores the importance of putting in place arrangements that can allow impartial supervision and monitoring," he said.An advance team of monitors in Syria had visited the town of Deraa and "enjoyed freedom of movement" there, Ban said. However, he noted that "the team's initial request to visit Homs was not granted, with officials claiming security concerns."