Russia has denied interfering with evidence at the site of the suspected Syrian chemical attack which led to Western air strikes on Saturday.
In an interview for BBC's Hardtalk, Russian Foreign Minister Sergei Lavrov said: "I can guarantee that Russia has not tampered with the site."
Concern about tampering was raised by the US envoy to the international chemical weapons watchdog.
International inspectors are trying to reach the site in Douma, near Damascus.
The UK's envoy to the watchdog, the OPCW (Organisation for the Prohibition of Chemical Weapons), has called for the inspectors to be given "unfettered access" to Douma, a town that was a rebel stronghold at the time of the attack on 7 April and is now under the control of the Syrian government and Russian military.
Speaking as the OPCW gathered in The Hague to discuss the crisis, Peter Wilson dismissed as "ludicrous" Russian suggestions that Britain had helped stage a fake attack.
In other developments:
- The US is expected to announce fresh economic sanctions against Russia
- EU foreign ministers meeting in Luxembourg said they understood the air strikes had had "the sole objective" of preventing further use of chemical weapons by the Syrian government
- UK PM Theresa May is to make a statement to Parliament after the opposition said it was wrong to have launched military action without consulting MPs
- The French parliament is to discuss the air strikes
What happened in Douma?
The suspected attack, denied by Syrian President Bashar al-Assad's government, reportedly killed dozens of people in Douma, in the Eastern Ghouta region.
Two bombs filled with chemicals were reportedly dropped several hours apart on the town.
Syrian medical sources say bodies were found foaming at the mouth, and with discoloured skin and cornea burns.
US sources said they had obtained blood and urine samples from victims which had tested positive for chlorine and a nerve agent.
What did Lavrov say exactly?
Kenneth Ward, US envoy to the OPCW, said: "It is our understanding the Russians may have visited the attack site.
EPA
"We are concerned they may have tampered with it with the intent of thwarting the efforts of the OPCW Fact- Finding Mission to conduct an effective investigation."
Speaking to the BBC, the Russian foreign minister denied chemical weapons had been used in Douma.
"I cannot be impolite with the heads of other states, but you quoted the leaders of France and the UK and US and, frankly speaking, all the evidence they quoted was based on media reports and social media."
The event did not take place, he said. "What did take place was the staged thing," he added.
Mr Lavrov also questioned why the US, UK and France had carried out their retaliatory air strikes before OPCW inspectors were able to visit the site.
AFP
Russia and the West, he added, were facing a situation worse than during the Cold War due to a lack of channels of communication
