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."
The Prime Minister has said 'the world should not stand idly by' after hundreds were killed in apparent chemical attacks in Syria last week.
Any UK military action in Syria would involve submarine-launched cruise missiles rather than air strikes, a military expert has predicted.