The United Nations humanitarian chief says the Syrian government has agreed to join UN agencies in a "limited assessment" of the situation, as government forces continue a crackdown on rebels.
Speaking at a news conference in Turkey on Friday, Valerie Amos said she had asked the Syrian government for unhindered aid access to the worst-hit areas, but it has requested more time.
Ms Amos again spoke of her shock at what she had seen in her visit this week in the Baba Amr neighbourhood of the city of Homs - a centre of opposition to President Bashar al-Assad's rule which rebel fighters left on 1 March after a 26-day siege, Reuters reports.
She said the area is totally destroyed and there are no people left.
The UN estimates at least 25,000 refugees have fled Syria in the past year.
UN-Arab League envoy Kofi Annan, who begins his peace mission in the capital Damascus on Saturday, has called for a negotiated political solution, but dissidents say there is no room for dialogue amid President Assad's crackdown.
Rifts among big powers have blocked any action by the UN to resolve the crisis, with China and Russia firmly opposing any measure that might lead to Libya-style military intervention.
Military officers flee to Turkey
Several senior Syrian military officers have defected and fled to Turkey.
The Turkish government has confirmed reports they were among 230 Syrians who crossed the border on Friday as a year-long crackdown on opposition groups continued.
Some 31 people were killed throughout Syria by government forces, including 17 in Homs, according to activists.
Tight media restrictions imposed by the authorities make it hard to assess conflicting accounts of events on the ground.