The United States "will respond" to a deadly chemical weapons attack in Syria regardless of whether the United Nations Security Council acts or not, U.S. Ambassador to the United Nations Nikki Haley said on Monday.
Haley also wants the council to vote Tuesday on a U.S. draft resolution to establish a new inquiry into who is to blame for using chemical weapons in Syria, diplomats said.
"We have reached the moment when the world must see justice done," Haley told the council.
The United States circulated a revised draft resolution to the 15-member council, which it first put forward on March 1, amid a warning from President Donald Trump that there would be a "big price to pay" for a suspected deadly poison gas attack on a rebel-held Syrian town on Saturday.
"History will record this as the moment when the Security Council either discharged its duty or demonstrated its utter and complete failure to protect the people of Syria," she said. "Either way, the United States will respond."
Haley said the UN Security Council's failure to act on Syria was normalizing the use of chemical weapons. "The great evil of chemical weapons use that once unified the world in opposition is on the verge of becoming the new normal."
Haley reprimanded Russia for its previous vetoes of proposed resolutions to condemn Syria for using chemical weapons, including the extension of a UN-mandated probe which previously pointed the finger at Bashar al-Assad's government.
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"Russia could stop this senseless slaughter if it wanted," Haley said, adding that this was the moment when the Council would either do its job or "demonstrate utter and complete failure to protect the people of Syria."
"Either way, the United States will respond," she said.
Russian U.N. Ambassador Vassily Nebenzia said on Monday that Moscow has warned the United States of "grave repercussions" if it carries out an attack against Syrian government forces over reports of a deadly chemical weapons attack.
"There was no chemical weapons attack," Nebenzia told the U.N. Security Council.
"Through the relevant channels we already conveyed to the U.S. that armed force under mendacious pretext against Syria - where, at the request of the legitimate government of a country, Russian troops have been deployed - could lead to grave repercussions," he said.
British U.N. Ambassador Karen Pierce told reporters ahead of the meeting that Britain "would prefer to start with a proper investigation," but all options were on the table and London was in close contact with its allies the United States and France.
Nebenzia also said that investigators with the global chemical weapons watchdog should fly to Syria as early as Tuesday to look into accusations about the attack, offering them protection from Syrian authorities and Russian troops.
"The Syrian authorities and Russian troops will provide conditions to travel to the areas of the alleged incident for them to familiarize themselves with the situation," he said.
The Organisation for the Prohibition of Chemical Weapons said it had opened an investigation to determine what exactly had happened in Douma.