The permanent members of the United Nations Security Council have held talks on a British resolution that could allow military action in Syria, but the meeting ended with no sign of an imminent vote.

Ambassadors from Russia and China, who fiercely oppose any military strike against Syrian President Bashar al-Assad's regime, left the closed-door negotiations after about 75 minutes on , according to the AFP news agency.

The US, British and French envoys carried on their talks but left the Council chamber without making any comment. The three countries were said to be considering a military strike over the alleged use of chemical weapons.

"Britain presented a text and the Russians repeated the arguments already made by their foreign minister," said one diplomat.

"The Russians and Chinese said they would refer the text to their governments. The talks are not over but there is no new meeting planned yet."

Britain, for its part, wants the Security Council to study findings from a team of chemical weapons inspectors currently in Damascus before backing any military action.

Britain, France and the United States say Assad's forces carried out a chemical weapon attack in the Damascus suburbs on August 21, reportedly leaving hundreds dead.

The Syrian government, backed by Russia, has blamed opposition rebels.

At a press briefing on Wednesday, US State Department spokeswoman Marie Harf acknowledged that the Council was unlikely to agree on any resolution, blaming Russia for the impasse.

"All previous attempts to get the Security Council to act on Syria have been blocked," she said, "and we cannot allow diplomatic paralysis to be a shield to the perpetrators of these crimes."

'Clear breach'

Earlier on Wednesday, NATO Secretary-General Anders Fogh Rasmussen said any use of chemical weapons was "unacceptable and cannot go unanswered", although he did not suggest any response.

"This is a clear breach of long-standing international norms and practice... those responsible must be held accountable," he said in a statement.

Britain's national security council also met on Wednesday and unanimously backed action against Syria, and Prime Minister David Cameron has recalled parliament from a summer recess for a debate on the crisis.

But Lakhdar Brahimi, the UN and Arab League envoy for Syria, said that international military action could be carried out only after it has been approved by the Security Council.

"I think international law is clear on this. International law says that military action must be taken after a decision by the Security Council," he told reporters in Geneva.

Syria has denied that it carried out the attack, and challenged world powers to provide evidence that it had done so. The Syrian ambassador to the United Nations, Bashar al-Jaafari, on Wednesday blamed the rebels for the attacks and said they were carried out with the help of Turkey, Saudi Arabia and Qatar.

"What we are saying, briefly speaking, [is] that these

terrorist groups obtained the materials of producing of the

chemical weapons from outside powers," he said.

Meanwhile, UN chemical weapons experts investigating the attack that killed hundreds of civilians in rebel-held suburbs of Damascus finished a second trip to Ghouta to take samples.

UN Secretary-General Ban Ki-moon said it would take the inspectors four days to finish gathering evidence, and they would then need time to analyse their findings.

Meanwhile, Iran's supreme leader, Ayatollah Ali Khamenei, said on Wednesday that US intervention in Syria would be "a disaster for the region", the ISNA state news agency reported.

"The intervention of supra-regional and foreign powers in one country will have no result other than lighting a fire and increase the hatred people have for them," the agency quoted Khamenei as saying.