BASHAR al-Assad has dismissed claims that Syrian forces were behind last week’s chemical weapons attack on civilians as a “100 per cent fabrication,” saying, rather, that America, in league with terrorists, was responsible.

In his first interview since the strike on the rebel-held town of Khan Sheikhoun in northern Syria, which killed 89 people, including babies, the Syrian President questioned if the pictures of dead children were real.

Noting how “you have a lot of fake videos now,” Assad told Agence France-Presse: “We don’t know whether those dead children were killed in Khan Sheikhoun. Were they dead at all? Who committed the attack if there was an attack?”

The President suggested Washington was behind the chemical weapons strike to enable it to launch a retaliatory attack.

“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,” he said.

Assad insisted his government had given up its arsenal of chemical weapons four years ago, noting: "Even if we have them, we wouldn't use them."

He accused the US of making up the claim that Damascus was responsible to enable it to carry out the retaliatory air strikes on a Syrian government airbase.

"It's stage one - the play we saw on social network and TVs - then propaganda and then stage two - the military attack."

Speaking from his office in the Syrian capital, Assad claimed Washington was "not serious" about ending the conflict, saying: "They want to use it as an umbrella for the terrorists."

The Syrian President made clear he would only allow an "impartial" investigation into the strike at Khan Sheikhoun to make sure it was not used for "politicised purposes".

Responding to Assad’s interview, Sir Malcolm Rifkind, the former Foreign Secretary, said: “It would be amusing if the whole events were not so tragic.

“Just think for a moment what Assad is asking us to believe. It’s not in dispute that the Syrian air force were attacking that town at the time this happened.

“We are asked to believe that by some extraordinary coincidence one of their bombs, one of their own conventional bombs, happened to land on a building in a town somewhere in northern Syria, which happened to be were part of the opposition stored their chemical weapons, which happened to explode causing the deaths and injuries. It’s ludicrous, it’s ridiculous; I don’t believe even the Syrians would believe it,” declared the Scot

Earlier, Theresa May said it was "highly likely" the Assad regime was behind the attack.

"Apart from anything else, we believe it's the only regime that has the capability to make such an attack," said the Prime Minister.

Turkey, which treated many of the wounded, stressed how it had "concrete evidence" the effects of sarin were found in the victims while scientists at Porton Down in Wiltshire also confirmed the deadly agent or a sarin-like substance was used in the attack.

Meantime, an American official told CNN the US military and its intelligence services had intercepted communications in which Syrian regime military figures and chemical experts spoke about preparations for the sarin attack.

Elsewhere, Jeremy Corbyn appeared to question whether the Syrian regime was responsible for the chemical weapons strike.

After Assad denied responsibility, the Labour leader called for an independent investigation to establish who did carry it out.

Pressed by reporters whether he believed it was possible the Assad regime was not responsible, Mr Corbyn said: "An investigation must take place as to who used those chemical weapons and when we find out who it is, it's a war crime and it should be then treated as such."

The party leader has already angered some Labour MPs after he condemned the retaliatory missile strike ordered by Donald Trump, warning it risked intensifying the conflict.