An air strike on a group of displaced Yemenis has killed at least 20 civilians, mostly from the same family, a UN statement and witnesses said Wednesday.

The attack on Tuesday afternoon hit a group of civilians in the Mawza district of the southwestern province of Taez, a statement by the UN refugee agency said.

Residents said the attack was carried out by a warplane from the Saudi-led coalition fighting Shiite rebels in support of Yemen's internationally recognised government.