The International Committee of the Red Cross said it was deeply concerned by accounts that a detention facility had been hit, and was sending medical teams and hundreds of body bags to the city of Dhamar.

The Saudi-led coalition said in a statement carried by the state-run Al-Ekhbariya news channel that it targeted a rebel "military position in Dhamar that stores drones and missiles".

"We took all precautionary measures to protect civilians," it added.

However, the Huthi television channel Al-Masirah said that "dozens were killed and injured" in seven air strikes that hit a building the rebels used as a prison.

Footage obtained by AFP showed heavy damage to the building, and several bodies lying in the rubble, as bulldozers worked to clear away huge piles of debris.

"We are taking these reports extremely seriously. I am on my way to Dahmar #Yemen to assess the situation," said Franz Rauchenstein, head of delegation for the ICRC in Yemen.

"We have visited detainees in this location before, as we do in other places as part of our work," he said on Twitter.

"An ICRC team carrying both urgent medical supplies that can treat up to 100 critically wounded persons and 200 body bags to be donated is on its way to Dhamar province #Yemen following air strikes which are reported to have killed or wounded dozens of detainees," the organisation added.

The coalition intervened in 2015 in support of the government after the Iran-aligned Huthis swept south from their northern stronghold to seize Sanaa and much of Yemen -- the Arab world's poorest nation.

The air strikes in Dhamar come after the coalition has been distracted in recent weeks by a battle for control of the south, which has pitted two of Riyadh's allies against each other.

Fighting over the past four years in Yemen has already claimed tens of thousands of lives and sparked what the United Nations calls the world's worst humanitarian crisis.