The Russian military has claimed an alleged chemical attack in Syria was staged and directed by Britain.
Volunteer first responders and activists said a chemical attack by the Syrian government killed more than 40 people in the town of Douma, which drew international outrage and prompted Washington and its allies to consider a military response.
Moscow warned against any strikes and threatened to retaliate.
The medics said none of the patients were hurt by chemicals.
Maj Gen Konashenkov said Britain was “directly involved in the provocation”.
Russia’s foreign minister Sergey Lavrov said earlier that Russian experts had inspected the site of the claimed attack and found no trace of chemical weapons.
As fears of a Russia-West military confrontation mounted, French President Emmanuel Macron expressed his “deep concerns” over the situation in Syria in a phone call with Russian President Vladimir Putin.
The Kremlin said Mr Putin warned against rushing to blame the Syrian government before conducting a “thorough and objective probe”.
The Russian leader warned against “ill-considered and dangerous actions … that would have consequences beyond conjecture”.
Mr Putin and Mr Macron instructed their foreign and defence ministers to maintain close contact to “de-escalate the situation”, the Kremlin said.
Nikki Haley told an emergency meeting of the UN Security Council called by Russia that should the US and its allies decide to act in Syria it will be to defend “a bedrock international norm that benefits all nations” — the prohibition on the use of chemical weapons.
She said “the United States estimates that (President Bashar) Assad has used chemical weapons in the Syrian war at least 50 times”.
On the suspected poison gas attack on Douma, Ms Haley said: “We know who did this. Our allies know who did this. Russia can complain all it wants about fake news, but no one is buying its lies and its cover-ups.”