A Saudi-led coalition air strike in Yemen killed nine members of the same family, including several children, on Sunday in the southwestern rebel-held city of Ibb, witnesses and medics said.

Eleven neighbours were also wounded when the family's house, on the southern edge of the mountain city, was hit during a night of intense air strikes, witnesses said.

Medics at the city's main hospital confirmed they had received nine bodies, including those of women and children.

The house was next to a vocational college that Iran-backed Huthi rebels have converted into a military base and arms depot, witnesses said.

The air strikes came amid growing international criticism of the Arab coalition over the mounting toll of civilian casualties in its campaign against the rebels.

Huthi rebels and troops loyal to former president Ali Abdullah Saleh control Ibb and swathes of Yemeni territory including the capital Sanaa, which they seized in September 2014.

Since the coalition intervened in March last year, government forces have managed to push rebels out of five southern provinces, including the port city of Aden.

More than 6,000 people have been killed in Yemen since the start of the Saudi-led campaign, more than half of them civilians, according to the United Nations.

The UN warned on Friday of rising civilian casualties, saying that 180 people were killed and 268 injured in August, a 40 percent rise on the previous month.

On Wednesday, at least 20 civilians died in air strikes on the rebel-held Red Sea city of Hodeida that the coalition said targeted "Huthi leaders".

UN chief Ban Ki-moon condemned the strikes on Hodeida, calling for "urgent measures to protect civilians and civilian infrastructure".