Britain's Armed Forces are drawing up plans for military action against Syria after the alleged toxic gas attack, which is said to have killed more than 1,300 people.

Prime Minister David Cameron, who is back in London after cutting his family holiday short, is deciding whether he will recall Parliament while he continues talks with international leaders on possible intervention.

Downing Street said Mr Cameron is considering what would constitute a "proportionate response". He is under pressure to be able to legally justify any intervention.