Dozens of people have been reported killed after US President Donald Trump ordered “decisive” military action against Houthi rebels in Yemen, opening a new salvo against the Iran-backed group that has targeted shipping lanes in the Red Sea.

The death toll from US strikes on Yemen has risen to 53, including five children, the Houthi rebels' health ministry said. The US said it launched a "decisive and powerful" wave of air strikes on Houthi targets on Saturday, with President Donald Trump citing Houthi attacks on shipping in the Red Sea as the reason.

The Iranian-backed rebels, who have targeted Israel and shipping in the Red Sea, said children were among those killed in the strikes ordered by President Trump.