Russian Federation on Saturday called for an emergency meeting of the United Nations Security Council as Moscow said it would consider supplying S-300 missile systems to Syria following US -led strikes. Lavrov did not offer evidence to back up his claim.
The day before a team from the worldwide chemical weapons watchdog was to arrive in Douma, east of Damascus, Mr Lavrov said Russian experts have inspected the site and found no trace of chemical weapons.
The United States is consulting with Britain and France about a joint military response to the attack in Douma that medics and rescuers said left at least 40 people dead on Saturday.
Moscow strongly warned against any strikes and threatened to retaliate.
As fears of a Russia confrontation with Western powers mount, French President Emmanuel Macron expressed his "deep concerns" over the situation in Syria in a phone call with Russian President Vladimir Putin.
Russia's envoy Nebenzia called on the United States, France and Britain "not to bring the world to such a risky threshold".
The US State Department said the United States has proof at "a very high level of confidence" that the Syrian government carried out the attack but is still working to identify the mix of chemicals used.
"The most important thing is to refrain from ill-considered and risky actions that would constitute a gross violation of the UN Charter and would have unpredictable consequences", the office of the president said in a statement after the call.
Mr Putin and Mr Macron instructed their foreign and defence ministers to maintain close contact to "de-escalate the situation", the Kremlin said.
The U.S. ambassador to the United Nations, Nikki Haley, said President Donald Trump "has not yet made a decision about possible actions in Syria".
U.S. intelligence shows a Russian claim that the attack was faked was false, Sanders said. Russian officials - both from Moscow and speaking at the United Nations - alleged quickly after Saturday's suspected attack that the images of the victims in Douma were fake.
The action followed a week of threats of retaliation for an alleged chemical weapons attack on civilians in Douma, outside Damascus, where Syrian forces have always been battling rebels.
Russian Federation responded angrily to a US -led strike against Syria on Friday, warning of unspecified "consequences" that stoked fears the conflict could escalate. "I hope no one would dare to launch such an adventure now", Lavrov said.
Russia, a key Syrian ally, dismissed the allegations against Syria and said its own experts found no "trace of chlorine or any other chemical substance used against civilians".
The capture of Douma has clinched a major victory for Mr Assad, crushing what was once a centre of the insurgency near Damascus, and underlines his unassailable position in the war, which entered its eighth year last month.
While insisting that the military action was a direct effect of the alleged chemical weapons attack in Douma, May also alluded to the use of a nerve agent in the English city of Salisbury.