Hague, who insisted Britain shared a common position with the US and France, told BBC Radio 4's Today program: "We have tried those other methods, the diplomatic methods, and we will continue to try those. But they have failed so far."

As no valid report has been reported by UN inspectors, the UK foreign secretary said that Britain effectively faced a stark choice between inaction or a military strike.

General Sir Nick Houghton, the chief of the defense staff, is to discuss military options with his US counterpart, General Martin Dempsey, and other allied military chiefs at a summit in the Jordanian capital of Amman.

Russia and China are likely to veto any UN Security Council resolution authorizing military action, but Hague said such a move could be legal under international law even without UN approval.

"It is possible to do that under many different scenarios," he said. "But anything we propose to do, the strong response we have talked about, whatever form that takes, will be subject to legal advice, must be in accordance international law."

The foreign secretary claimed that Britain's patience was wearing thin after all other forms of pressure on Syria had failed over the past year.

"Of course we want the maximum pressure from world opinion, from diplomatic work, on the Syrian regime not to do these things again. It has to be pointed out that such pressure does not appear to have worked," he said.

Hague's comments came after President Bashar al-Assad strongly denied using chemical weapons. He told Izvestia newspaper that: "Would any state use chemical or any other weapons of mass destruction in a place where its own forces are concentrated? That would go against elementary logic."

Assad added that military action would fail. In remarks reported by Reuters in Moscow, he said: "Failure awaits the United States as in all previous wars it has unleashed, starting with Vietnam and up to the present day".

NJF/NJF