The United Nations secretary-general says Syria has failed to comply with its obligation under a peace plan to pull troops and heavy weapons out of urban areas.
In a letter to the UN Security Council, Ban Ki-moon also called for an observer mission to be expanded from the small number already in the country to 300.
There are continued reports of violence in Syria, threatening the fragile week-old ceasefire, However, Mr Ban also said there was an "opportunity for progress", the BBC reports.
Meanwhile, US Secretary of State Hillary Clinton will meet foreign ministers in Paris on Thursday to discuss the crisis.
The peace plan, negotiated by UN-Arab League envoy Kofi Annan, aims to end more than a year of unrest thought to have killed at least 9000 people.
Mr Ban said it was critical that the Syrian government kept its pledge to withdraw troops from populated areas.
He said while the level of violence dropped markedly when the ceasefire began last Thursday, there had been an escalation in recent days, and breaches had been reported by both sides.
He also noted that there had been "no significant release of detainees", and "no substantive progress" in negotiations on humanitarian access, in reference to other aspects of Mr Annan's six-point plan.
Observers had been prevented from going to the city of Homs after the government cited "security concerns". But observers were allowed to visit the town of Deraa freely, he said.
