Saudi-led coalition air strike was carried out in the city of Dhamar, south of Yemen's capital Sanaa. Rebel spokesman Mohamed Abdul-Salam said a detention centre was hit but the coalition claimed it targeted a "military site".
More than 100 people are believed to have been killed when the Saudi-led coalition fighting Houthi rebels launched an air strike on a detention centre in Yemen, the International Committee of the Red Cross said on Sunday.
"We estimate over 100 people were killed," Franz Rauchenstein, head of delegation for the ICRC in Yemen, told AFP, adding that teams were working to find survivors under the rubble but that the chances "are very low".
Earlier, ICRC said it has sent "urgent medical supplies" to the area.
Franz Rauchenstein, head of the ICRC delegation in Yemen, said Sunday that he is heading to Dhamar "to assess the situation."
The Saudi-led coalition said in a statement the air strikes targeted a site storing drones and missiles.
Local residents, however, said it was a detention centre in the city that was hit.
"The prison is known to the coalition and the Red Cross, which visited the site several times," Abdul-Qadir al-Murtada, the head of a Houthi-run committee for prisoner affairs, said on Facebook.
The Houthi health ministry spokesman, in comments carried on the group's Al Masirah TV, said 60 bodies had been pulled from the rubble at the prison and that the number could rise.
There was no immediate independent confirmation on the exact number of casualties.
"The explosions were strong and shook the city," one resident said. "Afterwards ambulance sirens could be heard until dawn."
In 2015, a Houthi-run detention centre in Dhamar was struck by a Saudi-led coalition airstrike, killing at least 25 prisoners.
At the time, the Saudi-backed Yemeni government accused Houthi rebels of using prisoners as human shields.
Yemen has remained wracked by violence since 2014, when the Iran-aligned Houthi group overran much of the country, including the capital Sanaa.
The conflict escalated the following year when Saudi Arabia and its Sunni-Arab allies launched a massive air campaign aimed at rolling back Houthi gains in Yemen and supporting the country’s pro-Saudi government.
More than 70,000 people have been killed in the raging conflict since 2016, according to UN estimates.