"The Syrian claim is incorrect and likely intentional misinformation", he said in an email to Reuters. Turkey performed autopsies on three Syrians killed in the attack last week.
U.S. Ambassador to the UN Nikki Haley criticized Russian Federation for denying the UN-led investigation and blocking a resolution that would have helped promote peace in Syria.
Russian Federation accused the USA of breaking worldwide law with the attack against the Syrian regime, a key ally that Moscow has supported with air strikes since 2015.
But Assad doubled down on his denials in the interview with AFP, conducted on Wednesday and published on Thursday.
Assad, in an interview with Agence France-Presse, denied that any chemical weapons attack took place. It was not allowed to film the interview itself; instead, the encounter was filmed by the Syrian presidency.
When asked again if he thought the attack was a fabrication, Mr Assad replied, "Definitely, 100 per cent for us, it's fabrication". "Apart from anything else, we believe it's only the regime that has the capability to make such an attack".
Assad has consistently denied using chemical weapons at any point during Syria's six year civil war.
"We have never used our chemical arsenal in our history".
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Men between the ages of 55-69 are encouraged to discuss with their doctor about undergoing prostate cancer screening , the U.S. Since then, PSA screening rates have declined by as much as 10 percent, and now fewer than one-third of US men get the tests.
"Our impression is that the West, mainly the United States, is hand-in-glove with the terrorists", he said.
The chemical attack also invited deadly USA air strike on the Shayrat airfield of the Syrian air forces, believed by Washington to be the base for warplanes that carried out the chemical attack.
But Assad said evidence came only from "a branch of al-Qaeda", referring to a former jihadist affiliate that is among the groups that control Idlib province, where Khan Sheikhun is located.
"The director-general shared with the council the immediate steps taken by technical secretariat experts to analyze the available information and their preliminary assessment that this was a credible allegation", said the United Nations watchdog on chemical weapons.
"The strike was requested by the partnered forces, who had identified the target location as an ISIS fighting position", a coalition statement read, using an alternative acronym for IS.
Coughing, choking, foaming at the mouth, scores of panicked Syrians died in a recent chemical weapons strike. "They want to use it as an umbrella for the terrorists", said the Syrian president.
"You know that India is a signatory of the chemical weapons convention", External Affairs Ministry spokesperson Gopal Baglay said in weekly media briefing here.
Central Command said the strike was launched on Tuesday.