The United Nations hit back at Russian officials Wednesday for their claims that the UN report on the use of chemical weapons in Syria was “one-sided” and “political,” hours after Russia announced it would present to the UN Security Council alleged evidence that the rebels were behind the August 21 chemical attack in a Damascus suburb.

UN spokesman Martin Nesirky told reporters Wednesday that “the terrible facts speak for themselves,” and that UN Secretary-General Ban Ki-moon had the “fullest confidence” in the team.

Nesirky added that the UN was checking with Russia’s UN mission on the comments made by Deputy Foreign Minister Sergei Ryabkov about the UN inspectors.

“On the face of it these reported remarks are an attempt to call into question the secretary general’s investigation team led by Professor Ake Sellstrom and the credibility of its thoroughly objective report,” Nesirky said.

Earlier Wednesday, Ryabkov, who was in Damascus to meet with Syrian officials including President Bashar Assad, told the state-run Russian news agency RIA that Russia was “disappointed” with the report and the UN inspectors.

“We are disappointed, to put it mildly, about the approach taken by the UN secretariat and the UN inspectors, who prepared the report selectively and incompletely, ” he said.

“Without receiving a full picture of what is happening here, it is impossible to call the nature of the conclusions reached by the UN experts … anything but politicized, preconceived and one-sided,” he added.

A senior UN diplomat in New York said Wednesday that details on the scale of the attack, the rockets used and trajectory data cited in the report make it “abundantly clear” that the Syrian regime was behind the attack. The diplomat said: “There isn’t a shred of evidence in the other direction.”

The diplomat spoke on condition of anonymity because some of the material was from private meetings.

On Monday, UN inspectors said there was “clear and convincing evidence” that chemical weapons were used on a relatively large scale in the August 21 attack. The findings (click here to read the full report) represent the first official confirmation by scientific experts that chemical weapons were used in Syria’s civil war.

Russia has been Syria’s main ally since the start of the conflict in March 2011, blocking proposed UN resolutions that would impose sanctions on Assad’s regime and opposing an attempt to authorize the use of force if Syria does not abide by the agreement to get rid of its chemical weapons.

In the meeting between Ryabkov and the Syrian president Wednesday, Assad “expressed… his gratitude to Russia for its position of helping Syria face down the savage attack… and the Western, regional and Arab-backed terrorism,” AFP reported.

The UN inspectors’ team is due to return to Syria “within weeks” to complete the investigation it had started before the August 21 gas attack of other alleged chemical weapons attacks in the country.

Sellstrom told The Associated Press Wednesday the team will evaluate “allegations of chemical weapons use from both sides, but perhaps mainly from the Syrian government’s side.”

AP contributed to this report.