At least 20 civilians have been killed in an air strike by Saudi warplanes while attempting to escape Yemen, according to the UN and witnesses.

Survivors said a vehicle packed with families fleeing Saudi bombardments near the city of Taiz was hit on Tuesday. Officials said many of those killed were from the same family, including women and children.

The UN Refugee Agency (UNHCR) said it was shocked and saddened by the deaths in the Mawzaa district, where civilians had been displaced by intensified hostilities in the nearby port of Mocha.

Nowhere in Yemen safe for civilians, said UNHCR spokesperson Shabia Mantoo.

Each of Yemen's mainland governorates is affected by conflict and tens thousands have been killed and injured.

We have been advocating incessantly for respect of international humanitarian law and protection of civilians in Yemen. More must be done.

Ms Mantoo added that it was a travesty that civilians displaced by the conflict are being trapped in areas themselves hit by violence, with numerous sieges underway.

International rights groups have accused the Saudi-led coalition of bombing civilian gatherings, markets, hospitals, mosques and residential areas across Yemen since the beginning of its illegal aggression on Yemen in support of fugitive President Abdrabbuh Mansour Hadi in 2015.

Western countries especially the US and Britain are among key suppliers of weapons used by the Saudi regime to commit atrocities and war crimes in Yemen. These countries continue to back the Saudi regime despite opposition by citizens and human rights groups.

Saudi Arabia backed by the US and some despotic regional regimes launched the deadly campaign against Yemen in March 2015 to push back the popular Ansarullah movement from Sana'a and to bring back to power Abd Rabbuh Mansur Hadi, Yemen's president who has resigned and is a staunch ally of Riyadh.

The brutal aggression has so far claimed the lives of over 13,000 Yemenis mostly civilians including women and children. Additionally, a devastating cholera outbreak is ravaging the country with more than 330,000 suspected cases and 1,759 deaths reported between 27 April and 13 July in Yemen while daily bombardments by Saudi regime continue

The Saudi military aggression has also taken a heavy toll on Yemen's facilities and infrastructure, destroying many hospitals, markets schools, mosques and factories.