"Definitely, 100 percent for us, it's fabrication", he said of the incident.
Syria and Russian Federation have suggested a conventional airstrike by the Syrian army may have hit a depot storing chemical weapons possessed by extremists.
At least 87 people, including 31 children, were killed in the alleged attack, according to the Britain-based Syrian Observatory for Human Rights monitor.
Russian Federation on Wednesday vetoed a United Nations resolution demanding the Syrian government cooperate with an investigation into the alleged chemical attack, blocking Security Council action against its ally for an eighth time.
Even if we have them, we wouldn't use them.
FRENCH FOREIGN MINISTER JEAN-MARC AYRAULT, on claims by Syrian President Bashar al-Assad that "fake videos" and "propaganda" were being used against his government.
"We don't know whether those dead children were killed in Khan Sheikhun", he said.
The UK Ministry of Defense and Turkish authorities say they have carried out tests on samples that provide evidence that Sarin or a similar substance was used. US President Donald Trump said the attack was a response to the alleged chemical weapon use in Syria's Idlib, which Washington blames on the Syrian government.
It was the first direct United States military action against Assad's forces since Syria's civil war began six years ago, and led to a quick downward spiral in ties between Washington and Moscow.
Following last week's deadly attack, the Organisation for the Prohibition of Chemical Weapons said technical experts analysed the available information "and their preliminary assessment (was) that this was a credible allegation". But several experts have said that only the Syrian regime is likely to have stockpiles of Sarin gas.
Assad said no proper investigation had been possible because the area was controlled by Nusra Front.
Britain's Ambassador, Sir Geoffrey Adams, told the meeting that United Kingdom scientists have analyzed samples from Khan Shaykhun and they "tested positive for the nerve agent sarin, or a sarin-like substance".
The Syrian government s suspected chemical weapons attack on civilians last week amounts to a "war crime", the US State Department said Thursday.
Russia, Iran and Syria want an independent investigation and those opposed to the call "don't have a clear conscience", he said.
He added that "morally" the Syrian government would never do this "because it's not acceptable".