Talks at the United Nations over a response to the crisis in Syria will continue "over the coming days", Foreign Secretary William Hague said but he acknowledged that a new resolution was unlikely.
With Russia and China expected to veto any Security Council resolution for action against Syria, Mr Hague insisted the international community still had a responsibility to act even if agreement could not be reached in New York.
Mr Hague said: "This is the first use of chemical warfare in the 21st century. It has to be unacceptable. We have to confront something that is a war crime, something that is a crime against humanity.
"If we don't do so we will have to confront even bigger war crimes in the future and so we continue to look for a strong response from the international community that is legal, that is proportionate and that is designed to deter the further and future use of chemical weapons."