Nikki Haley told an emergency meeting of the UN Security Council called by Russian Federation that should the U.S. and its allies decide to act in Syria it will be to defend "a bedrock worldwide norm that benefits all nations" - the prohibition on the use of chemical weapons.
"We are confident that we have crippled Syria's chemical weapons program".
"Our president has not yet made a decision about possible action in Syria".
Russia's military says Britain was behind the alleged April 7 chemical attack that killed dozens of Syrians in a rebel-held suburb of Damascus.
"Without the sanction of the UN Security Council, in breach of the UN charter and the norms and principles of worldwide law, an act of aggression was committed against a sovereign state", the Kremlin said.
Earlier, French President Emmanuel Macron spoke by phone with Putin and expressed concern about a worsening situation.
Art Bell Dies on Friday the 13th at Age 72
He announced what would be his final retirement on December 11, 2015, citing security concerns at his home. The Nye County Sheriff's office Bell died in his Pahrump home yesterday.
"The military operation was necessary and appropriate to preserve the effectiveness of the worldwide ban on the use of chemical weapons and to warn the Syrian regime of further violations", she said in a statement voicing support for the joint US, UK and French action.
According to a statement by the French presidency, Mr Macron called for dialogue between France and Russian Federation to "continue and intensify" to bring peace and stability to Syria. US Ambassador Nikki Haley told the council "there is clear information demonstrating Assad's culpability". "We can not take such risks", he said at a forum. "Syria continues to engage in and provide a base for murderous actions, including those of Iran, that put its territory, its forces and its leadership at risk", the official said.
Moscow's UN ambassador Vassily Nebenzia told reporters after a private meeting of UN Security Council in NY that the immediate priority is to avert the danger of war. "The immediate priority is to avert the danger of war". "It would provoke a retaliation operation by government forces and the White Helmets were to use it to stage a provocation with an alleged use of chemical weapons", he said. France, the United Kingdom and the United States will brief allies on actions taken in Syria, the official said.
The Organisation for the Prohibition of Chemical Weapons (OPCW) fact-finding mission team are in Syria and are due to start work and research today.
After a crunch meeting with national security advisers on Thursday, the White House said he had not yet decided how to retaliate to last week's suspected chemical attack which the US, France and Britain blame on Bashar al-Assad's regime.
Assad, who is supported by Iranian-back fighters as well as the Russian air force, has cemented his control over most of the western, more heavily populated, part of the country.