Violence in Syria has continued despite a UN-backed deadline for a complete withdrawal of troops and weapons coming into effect.
Shelling was reported in Homs early on Tuesday, and there were clashes on the Turkish and Lebanese border overnight.
More than 100 people were killed on Monday, many of them civilians.
Damascus had agreed to the deadline but is demanding written guarantees its opponents will give up arms before ending its military action.
Under the plan - negotiated by the UN and Arab League's special envoy on the Syrian crisis, Kofi Annan - Syrian troops were to begin withdrawing from cities by Tuesday ahead of a full ceasefire coming into place on Thursday.
Earlier, United Nations secretary-general Ban Ki-moon called on the Syrian Government to immediately end attacks on civilians and honour the agreement brokered by Mr Annan.
United States state department spokesperson Victoria Nuland says the Syrian Government is stalling with demands that the opposition provide written guarantees it will stop fighting and disarm.