Britain will support any fresh retaliation by the US for the use of chemical weapons by Syria, Michael Fallon has said, after the White House revealed it had intelligence the regime was planning another attack.

The US said it had observed preparations at Shayrat air base, where jets which carried out a deadly sarin gas strike in April took off from. It warned Syria would pay a "heavy price" if it went ahead with such an assault.

Sir Michael, defence secretary, said that the UK backed the US administration of president Donald Trump when it mounted a Tomahawk missile strike against the regime following the attack on the rebel-held town of Khan Sheikhoun, which left 74 people dead, and was prepared to do so again.