In April past year, Shayrat airbase was targeted by US Tomahawk cruise missiles in a strike ordered by President Donald Trump in retaliation for a chemical weapons attack on Khan Sheikhun in Idlib in north-western Syria.
It was not known who carried out the attack, with Pentagon spokeswoman Heather Babb saying: "There are no USA or coalition operations in that area".
Syrian state TV carried live images of hourslong street celebrations with people dancing and chanting in support of their government's "steadfastness" following unprecedented joint airstrikes by the United States, France and Britain on Syria.
The OPCW team has so far held meetings with Syrian officials but is not believed to have started field work in Douma, where holdout rebels surrendered their weapons and agreed to leave after the alleged attack.
He claimed inspectors can not allowed access to the site without permission from United Nations security experts.More news: Alfie Evans' parents lose legal bid in attempt to save son
"The team has not yet deployed to Douma", Uzumcu told the organization's emergency talks. I'm sure Russian Federation will be providing that irrefutable proof any day now, just as soon as they finish scrubbing the Douma site of any evidence and blocking inspectors from doing their jobs.
The Kremlin dismissed the claims.
"I can guarantee that Russian Federation has not tampered with the site", he told the BBC.
He said Moscow has "irrefutable information that it was another fabrication".
It also slammed the United States, saying the weekend strikes on three facilities in Syria were a bid "to undermine the credibility" of the mission.
It marks one of the biggest victories yet for Syrian President Bashar al-Assad.More news: California rejects Trump administration plan for National Guard troops on border
The army said that troops discovered weapons factories, arms depots, tunnels and food storage places. Western states have used those videos as proof of Damascus' involvement in the alleged chemical attack in order to launch strikes against Syria.
Regime forces have since entered Douma and declared the entire Eastern Ghouta region around it fully retaken, ending a five-year siege and reclaiming an opposition bastion on the edge of the capital.
Even though the OPCW team was not allowed in, the Syrian authorities organised a tour of the town for the foreign press, including AFP.
The agency, set up to ensure the destruction of chemical armaments, is due to assess the scene and take samples from alleged attack victims to determine the cause and potentially uncover the perpetrators.
Russian Federation and the regime have both denied chemical weapons were used. "Suffocation cases arrived as a result of the debris, dust, fire and smoke".More news: Sexual assault survivors can now report anonymously through Manitoba community agencies