On Thursday the Syrian regime rejected a report by the Organization for the Prohibition of Chemical Weapons (OPCW) that said chlorine gas was used in an attack on the Syrian town of Douma last year.
The April attack on Douma, which was still under rebel control at the time, killed at least 40 people, according to activists.
In comments carried by state news agency, the Syrian Arab News Agency (SANA), a Foreign Ministry spokesman slammed the "fake reports which don't enjoy any credibility" and called on the OPCW "to appoint fact-finding mission members who are professional, fair and neutral."
"The Syrian Arab Republic, which offered all facilities to the [OPCW] mission team, hoped the mission would reach logical and professional conclusions away from any pressures or politicization, but it is regrettable the report was full of distortions of facts," the spokesman was quoted as saying.
Chlorine was used in an attack on the Syrian town of Douma in April 2018, although there was no evidence of a nerve agent, the OPCW said on Jan. 1 in a final report on the incident.
The world's chemical weapons watchdog said there were "reasonable grounds that the use of a toxic chemical as a weapon had taken place on April 7, 2018. This toxic chemical contained reactive chlorine."
The long-awaited findings confirmed an interim report released in July on the attack, which medics said killed about 40 people when a cylinder containing poison gas landed on the roof of a housing block.
The report does not place blame because it was not in the OPCW's remit at the time, although the watchdog has since been given powers to investigate responsibility for all chemical attacks in Syria back to 2014.
A team of OPCW inspectors took more than 100 samples from some seven sites in Douma when they gained access to the town several weeks after the attack.
The team also interviewed witnesses and carried out a series of tests including toxicological and ballistic analysis, said the watchdog based in The Hague.
Russia, which backs the regime of Syria's Bashar Assad, swiftly rejected the OPCW report, saying that it was "staged" by Syrian rescue volunteers known as the White Helmets.
"In spite of all the evidence presented by Russia, Syria, and even British journalists that the Douma incident is no more than a White helmets staged provocation, the Technical Secretariat of OPCW states in today's report that chlorine was used in Douma as a chemical weapon," the Russian Embassy in The Hague tweeted.
Despite rejections from the Syrian regime and Russia, activists and world powers have been accusing the Syrian regime of using chemical weapons against its opponents and civilians.
The suspected use of chemical weapons in Douma, located on the outskirts of Damascus, prompted the United States, Britain and France to mount a series of airstrikes on Syrian regime targets.
Separately, in Washington, the U.S. welcomed the OPCW's report from last week and slammed Syria and Russia for trying to "sow disinformation" and charged that both had falsely accused the opposition of being behind the attack in Douma.
"The United States rejects the efforts of the Assad regime and its supporters, Russia chief among them, to sow disinformation about alleged chemical weapons attacks," Robert Palladino, a spokesman, said in a statement, calling on Damascus to cooperate with the OPCW.