"It is our concern that they may have tampered with it with the intent of thwarting the efforts of the OPCW Fact-Finding Mission to conduct an effective investigation", said a United States official.
British Prime Minister Theresa May and French President Emmanuel Macron were both due to face their respective legislatures later in the day over their decision to join the USA in launching missiles at suspected chemical weapons sites in Syria, in an attempt to punish the Bashar al-Assad regime.
The comments came during a closed-door meeting at the Organisation for the Prohibition of Chemical Weapons, convened after an April 7 attack in the town of Douma, outside the Syrian capital, in which dozens of people were allegedly killed with poison gas.
"The alleged use of chemical weapons in Syria can not be a justification for military airstrikes in a territory of a sovereign state without the authorisation of the UNSC".
"Russia vows to shoot down any and all missiles fired at Syria".
The Kremlin dismissed the claims.
Russian Foreign Minister Sergei Lavrov said on Saturday that the Western countries' so-called proof of the purported use of chemical weapons by the Syrian government in the town of Douma was "ludicrous" for experts. "Therefore allegations of this towards Russian Federation are groundless", Peskov said.
Deputy Foreign Minister Sergei Ryabkov went as far as to say the inspectors were delayed because of the Western air strikes on Syria in retaliation to the chemical attack.
The inspectors were due on Monday to attempt to visit Douma, but the British delegation to the OPCW said they had not yet been granted access, citing the agency's director general.
In London, British Prime Minister Theresa May was facing criticism over her decision to bypass parliament and take part in the air strikes against Syria.
Inspectors have yet to visit Douma, where regimen troops and Russian police were deployed soon after the chemical attack which forced rebels there to surrender.
President Donald Trump said the strikes had accomplished their aim of undermining efforts by the Syrian government to produce and use chemical weapons again in violation of the Chemical Weapons Convention.
The strikes have ratcheted up global tension, as the USA and Russian Federation exchanged threats of retaliation.
"The Americans showed such a reaction when they felt that the terrorists were dislodged from an important region like Eastern Ghouta", Rouhani said in a phone call with Russian President Vladimir Putin on Sunday, a day after US-led strikes on Syria.
THE HAGUE (Reuters) - Russia may have tampered with the site of an alleged chemical weapons attack in Syria's Douma, the USA envoy to the global watchdog said on Monday, urging the body to condemn the continuing use of banned chemical weapons.
Douma was the last rebel holdout in the eastern Ghouta enclave, the target of a government offensive in February and March that left hundreds dead and tens of thousands homeless. The allies could not wait "to alleviate further humanitarian suffering caused by chemical weapons attacks", according to excerpts of her speech.