Foreign Secretary William Hague has said that the situation in Syria is "so grave, so serious and so rapidly deteriorating" that he cannot categorically rule out options including supplying arms to rebels and creating military safe havens.

"All our efforts are going into trying to ensure the [UN] Annan plan... is implemented. That is the best hope for Syria," he said.

Speaking to the Today programme's Justin Webb just before he began meetings with Syrian opposition leaders in Turkey, Mr Hague said it would be "rash" of anyone in Syria to think they can "forever escape accountability for these crimes".

The chances of President Assad being brought to justice "are rising all the time", he said.

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