A Downing Street spokesperson said:
“The Prime Minister spoke to President Trump about Syria this evening.
“They agreed that the Assad regime had established a pattern of dangerous behaviour in relation to the use of chemical weapons.
“They agreed it was vital that the use of chemical weapons did not go unchallenged, and on the need to deter the further use of chemical weapons by the Assad regime.
“They agreed to keep working closely together on the international response.”