US President Donald Trump has condemned the killing of dozens of civilians in northern Syria in an apparent chemical weapons attack by Syria’s air force.

It was an “affront to humanity”, he said, adding: “When you kill innocent children, innocent babies, little babies… that crosses… many lines.”

He did not mention Russia, Syria’s ally, which says chemical weapons in rebel hands may have been released.

But America’s envoy to the UN accused Russia of covering up for Damascus.