US President Donald Trump has ordered a series of air strikes on Yemen's capital, Sanaa, promising to use "overwhelming lethal force" until Iranian-backed Houthi rebels cease their attacks on shipping along a vital maritime corridor.

At least 16 people have been killed in a monster storm sweeping across much of the US.

Pope Francis is improving slowly as he battles double pneumonia in hospital and is reducing the use of mechanical ventilation at night to help with breathing, the Vatican said on Saturday.

At least nine Palestinians were killed, including two local journalists, and others wounded on Saturday in an Israeli airstrike on Gaza's northern Beit Lahiya town, Gaza's health ministry said, as Hamas' leaders hold Gaza ceasefire talks with mediators in Cairo.