An airstrike 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 recognized government.

The UNHCR said it was "deeply shocked and saddened at reports of the deaths and injuries of a number of internally displaced persons in an aerial attack" on the area.

The statement said the civilians had fled fighting in the nearby Mokha district, on the Red Sea coast.

Coalition-backed forces loyal to President Abedrabbo Mansour Hadi recaptured the port of Mokha in February as part of a major ongoing offensive to drive rebels from Yemen's lengthy coastline.

"This latest incident once again demonstrates the extreme dangers facing civilians in Yemen, particularly those attempting to flee violence, as they disproportionately bear the brunt of conflict," the statement said.

The coalition launched a military operation against the rebels in March 2015 as insurgents closed in on Hadi in his southern refuge in Aden forcing him to flee to Riyadh.

The World Health Organization estimates that more than 8,000 people have been killed in Yemen's conflict, most of them civilians, since March 2015.