The regime leader says peace talks on resolving Syria's war are ineffective because Washington is "not serious" about ending the conflict.
Syrian regime leader Bashar al Assad said on Wednesday that the chemical weapons attack on a rebel-held town, that killed more than 80 people and wounded at least 550 others, was a "fabrication" to justify a US military strike.
"Definitely, 100 percent for us, it's fabrication ... Our impression is that the West, mainly the United States, is hand-in-glove with the terrorists. They fabricated the whole story in order to have a pretext for the attack," Assad said in an exclusive interview with AFP in Damascus.
The United States responded to the chemical attack by firing 59 cruise missiles at a Syrian regime air base.
Assad said the barrage of US missiles against the airport had not diminished his regime's ability to carry out further strikes.
"Our firepower, our ability to attack the terrorists hasn't been affected by this strike," he said.
Earlier during the day, a delegation of British scientists at the Organisation for the Prohibition of Chemical Weapons (OPCW) in The Hague confirmed earlier testing by Turkish authorities that concluded that sarin gas had been used in the Khan Shaykhun attack.
The chemical weapons watchdog is also sending global chemical weapons investigators to Turkey as part of a fact-finding mission to gather biometric samples and interview survivors.
Syrian regime leader said peace talks on resolving the country's war were ineffective because Washington is "not serious" about ending the conflict.
"The United States is not serious in achieving any political solution. They want to use it as an umbrella for the terrorists," Assad said.
He said all chemical weapons stockpiles had been handed over in 2013, so the regime could not have been behind last week's attack.
"There was no order to make any attack … We gave up our arsenal a few years ago. Even if we have them, we wouldn't use them," he said.
The regime leader said that he would only allow an "impartial" external investigation of the chemical attack and added that, "We can 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."
Regime ally Russia on Wednesday vetoed a draft UN Security Council resolution demanding Syria cooperate with an international investigation of the attack.
Meanwhile, an air strike on Tuesday by the US-led coalition fighting Daesh mistakenly killed 18 members of the Syrian Democratic Forces (SDF) south of Tabqa city in Syria, the Pentagon said on Thursday.
"The strike was requested by the partnered forces, who had identified the target location as a Daesh fighting position," it said in a statement. "The target location was actually a forward Syrian Democratic Forces fighting position."