Gruesome scenes came to light as rescue workers pulled bodies from destroyed prison building and piled up mangled corpses, according to footage released by the Iran-backed Houthi rebels.
More than 100 people have been killed or wounded in an air strike on a Yemeni prison, rescuers have said after a night of deadly bombing underlined a dramatic escalation in violence.
Basheer Omar, spokesperson for the International Committee for the Red Cross in Yemen, said numbers were still rising following the attack on Friday in Saada, home city of the Houthi rebel movement.
"There are more than 100 killed and injured ... the numbers are going up," he said, citing figures at two Saada hospitals supported by the ICRC.
Taha Al Motawakel, health minister in the Houthi government, which controls the country's north, told The Associated Press in the capital, Sanaa, that at least 70 detainees were killed at the prison.
Further south in Hudaida, rebel video showed bodies in the rubble and dazed survivors after an air attack by the Saudi Arabia-led pro-government coalition took out a telecommunications hub.
Yemen suffered a nationwide internet blackout, a web monitor said.
Saada's hospital has received about 200 people wounded in the prison attack and "they are so overwhelmed that they cannot take any more patients", said Doctors Without Borders, known by its French acronym MSF.
"There are many bodies still at the scene of the air strike, many missing people," said Ahmed Mahat, MSF head of mission in Yemen.
"It is impossible to know how many people have been killed. It seems to have been a horrific act of violence."
The strikes come five days after the Houthis claimed a drone-and-missile attack on the United Arab Emirates that killed three people and prompted warnings of reprisals.
The United Nations Security Council condemned Houthi attacks ahead of its emergency session on Friday at UAE request.
The UAE is part of the Saudi-led coalition, which has been fighting the rebels since 2015, in an intractable conflict that has displaced millions of Yemenis and left them on the brink of famine.
Yemen's civil war began in 2014, when the Houthis descended from their base in Saada to overrun the capital Sanaa, prompting Saudi-led forces to intervene to prop up the government the following year.
Tensions have soared in recent weeks after the UAE-backed Giants Brigade drove the rebels out of Shabwa province, undermining their monthslong campaign to take the key city of Marib further north.
On January 3, the Houthis hijacked a United Arab Emirates-flagged ship in the Red Sea, prompting a warning from the coalition that it would target rebel-held ports.
And on Monday, they claimed a long-range attack that struck oil facilities and the airport in the UAE capital Abu Dhabi, killing two Indians and a Pakistani, and wounding six other people.
The attack — the first deadly assault acknowledged by the UAE inside its borders and claimed by the Houthis — opened up a new front in Yemen's war and sent regional tensions soaring.
In retaliation, the coalition carried out air strikes against rebel-held Sanaa that killed 14 people.
Yemen's civil war has been a catastrophe for millions of its citizens who have fled their homes, with many close to famine in what the UN calls the world's worst humanitarian crisis.
The UN has estimated the war has killed 377,000 people by the end of 2021, both directly and indirectly through hunger and disease.