The only information available concerning the chemical attack was falsified and published by al Qaeda, claims the Syrian president.
He said the entire incident was "fabricated" and "unconvincing".
Syrian President Bashar Assad speaks in an earlier interview with AFP, in February 2016 in Damascus.
"There was no order to make any attack ... we gave up our arsenal a few years ago".
Other world powers have also condemned Assad for the April 4 attack - although Syrian ally Russian Federation continues to maintain there is insufficient evidence Assad carried out the attack.
A suspected April 4 chemical attack in civil war-ravaged Syria killed almost 90 people and is under OPCW investigation.
"Our impression is that the West, mainly the United States, is hand-in-glove with the terrorists", Assad said, according to the wire service. "Were they dead at all".
When asked again if he thought the attack was a fabrication, Mr Assad replied, "Definitely, 100 per cent for us, it's fabrication".
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Russian and Syrian government strikes have increased by 20 percent in the week since the USA hit a Syrian air base, according to figures from the Syrian Network for Human Rights (SNHR), with at least 98 civilians killed.
He said Khan Sheikhun had no strategic value and was not now a battle front.
"The strike was requested by the partnered forces, who had identified the target location as a Daesh fighting position", it said in a statement.
And Assad said he could "only allow any investigation when it's impartial, when we make sure that unbiased countries will participate in this delegation in order to make sure that they won't use it for politicised purposes". The United States, Turkey and other Western states have blamed the Assad regime for the deaths. "Furthermore, we noticed a rise in the rates of the use of cluster munitions, incendiary weapons, and barrel bombs", the report states.
Writing for the Daily Sabah, Kalin evaluated the recent incidents in Syria following the regime's chemical attack in Idlib on April 4.
Dujarric said that the joint investigation mechanism, once it starts its work, will try to find the perpetrators of the attack, rather than establish what type of chemicals was used.
The chemical attack also invited deadly US 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.
They have said the attack which killed more than 80 people was either a rebel provocation or the result of Syrian planes hitting a rebel weapons factory.