At the same time the Syrian government, which has denied accusations by a range of Western and Arab countries that it had used the weapons in the Aug. 21 mass killing, moved abruptly to prolong the visit of the United Nations inspectors, announcing it had evidence of three previously unreported chemical weapons assaults that they should investigate.

Taken together, the developments had the effect of slowing, for the moment, the momentum for military action led by the United States and Britain. Both have said the evidence is already persuasive that the government President Bashar al-Assad of Syria used chemical munitions on civilians in the Damascus suburb of Ghouta last week, committing what the Obama administration has called a moral atrocity that cannot go unanswered.

While the United States could still act unilaterally, the Obama administration has actively sought to build a consensus for a military strike, and Britain is the closest American ally.

The British signal that it would not rush to military action came late Wednesday when the government of Prime Minister David Cameron, aware of the sensitivities created by the rush to war in Iraq a decade ago, altered the language of a motion to be voted on by Parliament on Thursday so that a separate vote on military action would be required. That vote may not take place until next week.

The resolution states that “a United nations process must be followed as far as possible to ensure the maximum legitimacy for any such action.” The resolution also states that the secretary general “should ensure a briefing to the United Nations Security Council immediately upon the completion of the team’s initial mission.”

Mr. Cameron’s pullback came as Britain moved to introduce a resolution at the United Nations Security Council that would authorize military action in Syria — a measure that Russia, the Syrian government’s most important backer, quickly signaled it would block.

After an informal meeting among the five permanent Security Council members at the United Nations headquarters in New York, no further action on the British resolution was taken, and one Western diplomatic source said “this isn’t going anywhere.”

The Russians argued that it was premature to even talk about such a resolution while United Nations inspectors were on the ground in Syria.

Syria’s ambassador to the United Nations, Bashar Jaafari, added a new level of complexity to the issue on Wednesday, announcing that he had submitted evidence of three previously unreported instances of chemical weapons use in Syria, which he asserted had been carried out by Syrian insurgents.

Mr. Jaafari said the new instances occurred on Aug. 22, 24 and 25, and were also in the Damascus suburbs. He said Syrian soldiers were the targets. The ambassador did not explain why he was only now bringing forth the allegations.

Mr. Jaafari repeated the Syrian government’s denials that it had ever used chemical weapons in the conflict and said the accusations were a conspiracy by Western nations acting on Israel’s behalf. He rejected assertions by the United States, Britain and other Western allies that there was persuasive evidence of Syrian government culpability in the use of the banned weapons.

“We are not warmongers,” he told reporters outside the Security Council chambers. “We are a peaceful nation seeking stability. The Syria government is totally innocent of these accusations.”

In Washington, the State Department spokeswoman, Marie Harf, suggested that the failure of Britain’s Security Council resolution to move forward had been expected.

In a separate declaration after discussions at NATO, the alliance’s secretary general, Anders Fogh Rasmussen, also sharply criticized Mr. Assad’s government, saying that “information available from a wide variety of sources points to the Syrian regime as responsible for the use of chemical weapons in these attacks.”

“This is a clear breach of longstanding international norms and practice. Any use of such weapons is unacceptable and cannot go unanswered. Those responsible must be held accountable,” the statement added. But Mr. Rasmussen gave no indication that NATO was contemplating any specific action.

Earlier Wednesday, Russian officials continued to warn against international intervention. The foreign minister, Sergey V. Lavrov, spoke by telephone with the United Nations special envoy to Syria, Lakhdar Brahimi, and warned that an attack “will only lead to the further destabilization of the situation in the country and the region,” according to a statement posted by the Foreign Ministry.

For his part, Mr. Brahimi told reporters in Geneva on Wednesday that international law required Security Council approval for any military action in Syria. Mr. Brahimi also said the United States and Britain had yet to share what they said was evidence that established Mr. Assad’s government had used chemical weapons.

In a further sign of mounting tensions, Russia’s Emergency Services Ministry said it was evacuating more Russians and citizens from other former Soviet republics from Syria, where Moscow maintains a naval base and where thousands of its citizens live after decades as the main international sponsor of the government in Damascus.

Russian special flights, sent to Syria with humanitarian supplies, returned with scores of Russians and citizens of Belarus and Ukraine. The Emergency Services Ministry said 75 Russians, along with nine people from Belarus and five from Ukraine, arrived in Moscow late Tuesday, while a second plane carrying 27 more Russians arrived on Wednesday morning.

Russia began evacuating its citizens from Syria in January. Since then 730 have left, most of them women and children. They are only a fraction of the more than 30,000 Russians who are believed to live in Syria, but in the wake of the attacks outside of Damascus, the pace of the evacuations appears to be increasing. 

Source:The New York Times