The Syrian government has handed Russia new materials implicating rebels in a chemical attack outside Damascus on August 21, Sergei Ryabkov, the Russian deputy foreign minister, said after talks in Damascus.
Ryabkov also said on Wednesday that his country was disappointed with the UN report on the chemical weapons attack published this week, saying it was selective and had ignored other episodes.
"The corresponding materials were handed to the Russian side. We were told that [it was] evidence that the rebels are implicated in the chemical attack," Ryabkov was quoted as saying by Russian news agencies after talks with Walid al-Muallem, the Syrian foreign minister, late on Tuesday.
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He said that Russia would "examine the Syrian materials implicating the rebels with the utmost seriousness".
To the fury of the West, Russia has repeatedly expressed suspicion that the chemical attack was a "provocation" staged by the rebels with the aim of attracting Western military intervention in the conflict.
"Without a full picture... we cannot describe the character of the conclusions as anything other than politicised, biased and one-sided," he said.
The US and France blame the Syrian government for the attack, which Washignton says killed 1,429 people including hundreds of children.
"When you look at the details of the evidence they present - it is inconceivable that anybody other than the regime used it," US President Barack Obama said on Tuesday.
Ryabkov is on a visit to Damascus to present the Syrian regime with the results of the agreement between Moscow and Washington reached in Geneva at the weekend to rid Syria of its chemical weapons.
He said he emphasised to Muallem the importance of the Syrian side "strictly and swiftly" handing over details of its chemical weapons arsenal to the Organisation for the Prohibition of Chemical Weapons, the first step in the agreement.
'No military action'
The Russia-US agreement is aimed at warding off the threat of US-led military action as retribution for the chemical attack.
The Syrian ambassador to Moscow, Riyad Haddad, told the Interfax news agency that Ryabkov was expected to have a meeting on Wednesday with President Bashar al-Assad.
Ryabkov said he assured the Syrian side that there was "no basis" for a UN Security Council resolution on the chemical weapons agreement to invoke Chapter VII of the UN Charter that allowed the use of force and tough sanctions.
He said this could only be considered if the UNSC was able to confirm violations of the convention on chemical weapons. "This is a hypothetical situation."
"It is especially important that some kind of political interests do not again appear, especially in New York [at the UN]," he added.
In the UN report, released on Monday, investigators found "clear and convincing evidence'' that chemical arms were used on a relatively large scale in the attack.
As expected, the report did not say who launched the attack in rebel-held Damascus suburbs.