President Donald Trump’s National Security Adviser said on Monday the United States, Britain and France had agreed that any further use of chemical weapons by Syria would prompt a “much stronger response” compared to previous air strikes.

In recent days American officials have said they believe government forces are preparing to deploy chemical weapons ahead of an assault on the rebel-held enclave of Idlib.

"We've tried to convey the message in recent days that if there's a third use of chemical weapons, the response will be much stronger,” said John Bolton, in his first speech since joining the White House.

"And I can say we've been in consultation with the British and the French, who joined us in the second strike, and they also agree that another use of chemical weapons will result in a much stronger response.”

Jeremy Hunt, the Foreign Secretary, Gavin Williamson, the Defence Secretary, and Mark Sedwill, the National Security Adviser, are all understood to have been involved in discussions about the appropriate response in the event of another chemical weapons attack in Syria.