French Foreign Minister Jean-Marc Ayrault said French intelligence services would provide proof of that in the coming days.
On April 4, a chemical weapons incident in Syria's Idlib province claimed the lives of some 80 people and inflicted harm on an additional 200 civilians.
"We don't know whether those dead children were killed in Khan Sheikhoun", he said in an interview with AFP TV.
However, Washington came to the conclusion that Damascus had used chemical weapons which led the U.S. to carry out a missile attack on the Syrian military's Shayrat air base located in the Homs Governorate on April 7, as the United States believes that the attack on Khan Shaykhun was launched from there.
Syria disclosed its chemical weapons stockpile amounted to some 1,300 tons of sarin, VX nerve agent and mustard gas, among other chemical agents.
He said he couldn't provide evidence now because analysis is still underway but added: "In a few days I'll be able to provide proof".
"We formally sent a letter to the United Nations, we asked them in that letter to send a delegation in order to investigate what happened in Khan Shaykhun", Assad said.
Western nations have accused the Syrian regime of carrying out the suspected air strike, but Moscow, the closest ally of Syrian President Bashar al-Assad, has sought to clear the regime of blame.
In an unprecedented step, the OPCW's executive council in November condemned Syria's use of toxic weapons - the council's first public condemnation of a member of the Chemical Weapons Convention.
"The likelihood of exposure to a chemical attack is amplified by an apparent lack of external injuries reported in cases showing a rapid onset of similar symptoms, including acute respiratory distress as the main cause of death", World Health Organization said in its statement on 5th April.
The convoy of buses containing 3,000 evacuees, a mix of pro-regime fighters and residents from government-held Foua and Kefraya, was halted near the rebel-held transit point of Rashidin on the outskirts of Aleppo yesterday, due to heightened security measures following Saturday's deadly attack on a previous convoy.
Moscow last week vetoed a UN Security Council resolution demanding a swift investigation into the attack - the eighth time Russian Federation has used its veto to protect the Assad regime since bloody civil war erupted in Syria in 2011.
The governing body of the global chemical arms watchdog is expected to vote on a fresh investigation.
On Friday Russian Foreign Minister Sergei Lavrov criticized the OPCW for not sending experts to the attack site, saying it was "unacceptable to analyze events from a distance".
In response, OPCW director general Ahmet Uzumcu said a team was ready to head to the town "should the security situation so permit".