Syrian president Bashar al-Assad has accused the US of fabricating last week’s chemical attack to justify a military strike, even as British investigators confirmed the use of toxic sarin gas.

In his first interview since the attack on the northern opposition-held town of Khan Sheikhoun which left 86 dead and hundreds injured, Assad said his regime could not be responsible as they were no longer in possession of any chemical weapons.

"Our impression is that the West, mainly the United States, is hand-in-glove with the terrorists,” Mr Assad told AFP news agency, referring to rebels which control the area. “They fabricated the whole story in order to have a pretext for the attack.

"It's stage one, the play [they staged] that we saw on social network and TVs, then propaganda and then stage two, the military attack," he said, questioning the authenticity of the video footage which drew international outrage.