UK Foreign Secretary William Hague says he believes President Assad was behind a chemical attack in Syria.

"I know that some people in the world would like to say that this is some kind of conspiracy brought about by the opposition in Syria," said Mr Hague.

"I think the chances of that are vanishingly small and so we do believe that this is a chemical attack by the Assad regime."

It was "not something that a humane or civilised world can ignore".