Assad said Syria, which is a signatory to the worldwide Chemical Weapons Convention, would accept an "impartial" chemical attack probe to investigate the accusations against him.
The United States and its allies say the Syrian military carried out the Idlib attack, something Syria has already denied.
Catholic leaders have spoken out against the USA response to the deadly chemical attack in Syria last week, saying investigations should have been conducted before the missile strikes on an air base believed to be the origin of the deadly chemical weapons attack.
In the interview, Assad insisted it was "not clear" whether an attack on Khan Sheikhun had even happened. We don't know if they were dead or who committed the attack.
US Central Command said coalition aircraft were given the wrong coordinates by their partner forces, the predominantly-Kurdish Syrian Democratic Forces, for a strike meant to target IS militants south of their Tabqa stronghold, near the extremists' de facto capital, Raqqa.
Lavrov said that his colleagues from the US, France and Britain "do not pay attention to the fact that you have to visit not only the airbase which is suspected as the place where chemical weapons were loaded on planes, but also the place where affected these weapons".
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CNN reporters point out that their news organization actually interviewed victims, and the news organization and many others also report that USA military and intelligence officials intercepted communications implicating the Syrian military ahead of the attack.
Spokesman Mark Toner also ridiculed the Syrian president's comments to AFP, describing them as "vintage Assad".
Another senior USA official told the AP on condition of anonymity earlier this week that initial U.S. investigations have concluded that Russian Federation was aware in advance of the suspected chemical strike.
Assad said he would only allow an "impartial" external investigation involving "unbiased countries", according to AFP.
Also on Wednesday, Russia's representative to the United Nations vetoed a Security Council resolution condemning the attack and calling for an immediate global investigation.
The US strike on the Syrian air base was the first time Washington has deliberately and directly targeted the Syrian government.