A number of Somali refugees were killed when their boat was hit in an air strike off the coast of Yemen, the UN says.

At least 31 people died in the incident, news agencies reported, quoting officials in Hudaydah port.

Women and children were among those killed when the vessel was attacked near the Bab al-Mandeb strait, the port officials said.

Images from the scene showed a boat strewn with bodies.

The refugees were on their way from Yemen to Sudan when they were attacked by an Apache helicopter near the strait, coastguard Mohamed al-Alay told Reuters.

It was not clear who carried out the attack. The port is controlled by Houthi rebels who are fighting a Saudi-led coalition in Yemen's two-year war.