The Russians also escalated their critiques of Western governments' interpretations of the UN report, which offered the first independent confirmation of a large chemical-weapons assault August 21 on the outskirts of the Syrian capital, Damascus, that asphyxiated hundreds of civilians.

Although the report did not assign blame for that assault to either side in Syria's civil war, analyses of some of the evidence it presented point directly at elite military forces loyal to Syria's president, Bashar al-Assad. The US, Britain, France and human rights and nonproliferation groups also say that the report's detailed annexes on the types of weapons used, the large volume of poison gas they carried, and their trajectories all lead to the conclusion that the forces of Dr Assad were culpable.

The Russian criticism came as the five permanent members of the Security Council began a second day of negotiations at the UN on a draft resolution aimed at ensuring that the Syrian government honours its commitment to identify and surrender all chemical munitions for destruction, as it officially agreed to do under a deal negotiated by Russia and the United States that averted a punitive US missile strike on Syria.

Russian news reports quoted the country's deputy foreign minister, Sergey Ryabkov, as saying during a visit to Damascus that the Syrian government had provided additional information that showed that insurgents used chemical weapons not only on August 21, but also on other occasions.

The Syrians offered no such information to the UN chemical weapons inspectors before they left Syria with a trove of forensic samples. The weapons inspectors have said they would return to Syria to investigate other alleged instances of chemical weapons use, but no dates have been announced.

Mr Ryabkov spoke after meeting with Dr Assad and his foreign minister, Walid al-Moallem. He did not disclose the precise nature of the additional information the Syrians had conveyed to him, but he was blunt about in his criticism of the UN report.

"We are unhappy about this report," Mr Ryabkov said in remarks broadcast by the state television network, RT. "We think that the report was distorted. It was one-sided. The basis of information upon which it is built is insufficient." He also said Russia needed "to learn and know more on what happened beyond and above that incident of August 21."

His remarks came a day after Russia's foreign minister, Sergey Lavrov, also questioned the UN report, although not as harshly. Mr Lavrov, who brokered the agreement with US Secretary of State John Kerry to put Syria's chemical weapons under international supervision, said on Tuesday that there were still "serious grounds to believe" that the August 21 attack was a provocation carried out by the rebel side.

Asked about the Russian criticisms, Martin Nesirky, a spokesman for UN Secretary-General Ban Ki-moon, said it had been clear to everyone that the chemical weapons inspectors were focusing first on the August 21 attack because of its magnitude and were planning to return to Syria to investigate other suspected assaults involving chemical munitions, with a more comprehensive report to be compiled thereafter.

Mr Nesirky also took issue with the Russian portrayal of the report as biased.

"The findings in that report are indisputable. They speak for themselves," he told reporters at a daily midday briefing. "This was a thoroughly objective report on that specific incident."

Russia, which like the other permanent Security Council members has veto power over any resolution, is resisting coercive language in the draft offered by the Western members that could lead to military intervention in Syria.

The Russian position, despite evidence that others say is abundantly damning of Dr Assad's forces, appeared intended to sow enough doubt to call into question additional pressure on Syria's government, and perhaps to cloud evidence that at least some of the country's arsenal was of Soviet origin.

President Vladimir Putin also asserted in an op-ed article in The New York Times last week that there was abundant evidence to believe that the rebels had carried out an attack using chemical weapons to force international intervention.

New York Times