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 a fragile ceasefire that began a week ago.
However, Mr Ban also said there was an "opportunity for progress".
Meanwhile, US Secretary of State Hillary Clinton will meet foreign ministers in Paris later 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 9,000 people.