The UK is to put a resolution to the UN Security Council later on Wednesday, August 28 "authorising necessary measures to protect civilians" in Syria, BBC News said.

The resolution will be put forward at a meeting of the five permanent members of the council, UK Prime Minister David Cameron said on Twitter.

Earlier a team of UN weapons inspectors resumed work probing a suspected chemical weapons attack on 21 August.

UN Secretary General Ban Ki-moon called on the council to act together. "The body interested with maintaining international peace and security cannot be 'missing in action'," Ban said. "The council must at last find the unity to act. It must use its authority for peace," he went on.

Cameron said in another message: "We've always said we want the UN Security Council to live up to its responsibilities on Syria."

"Today they have an opportunity to do that," he said. The draft resolution would condemn the "chemical weapons attack by Assad", he added.

Cameron will chair an emergency meeting of the UK's National Security Council at midday local time (11:00 GMT) to discuss possible responses to the crisis.

Meanwhile, in a briefing to journalists, joint UN-Arab League envoy to Syria Lakhdar Brahimi said: "It does seem clear that some kind of substance was used... that killed a lot of people" on 21 August. But he emphasised that any military action needed Security Council authorization.