Western countries have accused Moscow of preventing inspectors from reaching the site of a suspected poison gas attack in Syria and say Russians or Syrians may have tampered with evidence on the ground.
- The US has told the global watchdog that Russia may have tampered with the site
- Russia's Foreign Minister has denied the allegations
- The UK says inspectors have not been granted access to the sites yet
The United States, Britain and France launched air strikes on Saturday against what they described as three Syrian chemical weapons targets in retaliation for a suspected gas attack that killed scores of people in the Damascus suburb of Douma on April 7.
Syria and its ally Russia deny using poison gas during their offensive this month, in which they seized the town that had been the last major rebel stronghold near the capital.
Inspectors from the Organisation for the Prohibition of Chemical Weapons (OPCW) went to Syria last week to inspect the Douma site but have yet to gain access to the town, which is now under government control after the rebels withdrew.
"It is our understanding the Russians may have visited the attack site," US ambassador Kenneth Ward said at a meeting of the OPCW in The Hague on Monday.
"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."
His comments at the closed-door meeting were obtained by Reuters.
Russian Foreign Minister Sergei Lavrov denied that Moscow had interfered with any evidence.
"I can guarantee that Russia has not tampered with the site," he told the BBC in an interview.
Earlier, Britain's delegation to the OPCW accused Russia and the Syrian Government of preventing the international watchdog's inspectors from reaching Douma.
The inspectors aim to collect samples, interview witnesses and document evidence to determine whether banned toxic munitions were used, although they are not permitted to assign blame for the attack.
"Unfettered access is essential," the British delegation said in a statement.
"Russia and Syria must cooperate."
But Moscow blamed the delay on the Western air strikes. Kremlin spokesman Dmitry Peskov said the British accusation that Russia was to blame for holding up the inspections was "groundless".
"We called for an objective investigation. This was at the very beginning after this information [of the attack] appeared," Mr Peskov said.
"Therefore allegations of this towards Russia are groundless."
May to face questions over Syria strikes
In the aftermath of the alleged chemical attack, the remnants of the rebel army evacuated, handing Mr Assad one of the biggest victories in a war that has killed about half a million people and laid waste to whole cities.
The US-led strikes did nothing to alter the strategic balance or dent Mr Assad's supremacy and the Western allies have said the aim was to prevent the further use of chemical weapons, not to intervene in the civil war or topple Mr Assad.
In London, British Prime Minister Theresa May is facing criticism over her decision to bypass parliament and take part in the air strikes.
Ms May will make a statement to parliament on her decision and will repeat her assertion that Mr Assad's forces were highly likely responsible for the attack.
The allies could not wait "to alleviate further humanitarian suffering caused by chemical weapons attacks", according to excerpts of her speech.
But she will be questioned over why she broke with a convention to seek parliamentary approval for the action, a decision that she and her ministers say was driven by the need to act quickly.
Jeremy Corbyn, leader of the main opposition Labour Party, has questioned the legal basis for Britain's involvement.
Britain has said there are no plans for future strikes against Syria, but Foreign Secretary Boris Johnson warned Mr Assad that all options would be considered if chemical weapons were used against Syrians again.