Russia has warned the US that launching air strikes in response to a suspected chemical attack in Syria could spark a war between the two countries.
“The immediate priority is to avert the danger of war,” Moscow’s UN ambassador Vassily Nebenzia said on Thursday.
He accused Washington of putting international peace at risk and said the situation was “very dangerous”.
Western powers are thought to be preparing for strikes but Russia, a Syrian ally, opposes such action.
“We cannot exclude any possibilities, unfortunately,” Mr Nebenzia told reporters after a private meeting of the UN Security Council in New York.
He said there was a heightened “danger of escalation” because of the Russian military presence in Syria.
Senior Russian figures, including the head of the military, have warned that US missiles will be shot down and their launch sites targeted if Russian personnel come under threat.
Mr Nebenzia also called for the UN Security Council to meet again on Friday to discuss the possibility of Western military action.
The White House says it is continuing to assess intelligence and talk to its allies on how to respond.
Meanwhile, the Organisation for the Prohibition of Chemical Weapons (OPCW) says experts are travelling to Syria and will start investigations on Saturday.