UN Secretary-General Ban Ki-moon says the Syrian government is responsible for guaranteeing UN observers full freedom of movement to monitor the country's tenuous ceasefire, which appeared to be unraveling as regime forces pounded the opposition stronghold of Homs, activists said.

Ban, speaking to reporters in Brussels, called on Assad to ensure the observers are not impeded in any way in their work.

"It is the Syrian government's responsibility to guarantee freedom of access, freedom of movement within the country,'' he said Monday.

"They should be allowed to freely move to any places where they will be able to observe this cessation of violence."

He called the cease-fire "very fragile'', but said it was essential that it hold so that an "inclusive political dialogue can continue".

He said opposition forces "should also fully cooperate".

[Source:AP]