The Huthi rebels released gruesome video footage showing bodies in the rubble and mangled corpses from the prison attack, which levelled buildings at the jail in their northern heartland of Saada.

Further south in the port town of Hodeida, the children died when air strikes by the Saudi-led coalition hit a telecommunications facility as they played nearby, Save the Children said. Yemen also suffered a country-wide internet blackout.

"The children were reportedly playing on a nearby football field when missiles struck," Save the Children said.

The attacks come five days after the Huthis took the seven-year war into a new phase by claiming a drone-and-missile attack on Abu Dhabi that killed three people.

The United Arab Emirates, part of the Saudi-led coalition fighting the rebels, threatened reprisals.

Aid workers said hospitals were overwhelmed in Saada after the prison attack, with one receiving 200 wounded, according to Doctors Without Borders.

Basheer Omar, spokesperson for the International Committee for the Red Cross in Yemen, told AFP: "There are more than 100 killed and injured... the numbers are going up."

- 'Horrific act' -

Ahmed Mahat, Doctors Without Borders' head of mission in Yemen, said: "There are many bodies still at the scene of the air strike, many missing people."

"It is impossible to know how many people have been killed. It seems to have been a horrific act of violence."

The United Nations Security Council is due to meet at 1500 GMT on Friday in an emergency session on the Huthi attacks against the UAE, at the request of the Gulf state, which has occupied one of the non-permanent seats on the council since January 1.

The UAE is part of the Saudi-led coalition that 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.

The coalition claimed the attack in Hodeida, a lifeline port for the shattered country, but did not say it had carried out any strikes on Saada.

Saudi Arabia's state news agency said the coalition carried out "precision air strikes... to destroy the capabilities of the Huthi militia in Hodeida".

- 'Collapse of internet' -

Global internet watchdog NetBlocks reported a "nation-scale collapse of internet connectivity". AFP correspondents in Hodeida and Sanaa confirmed the outage. Save the Children said it would hamper its operating capacity.

Yemen's civil war began in 2014 when the Huthis 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 months-long campaign to take the key city of Marib further north.

On January 3, the Huthis 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 Huthis -- 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 killed 377,000 people by the end of 2021, both directly and indirectly through hunger and disease.

UAE presidential adviser Anwar Gargash warned the country would exercise its right to defend itself after the Abu Dhabi attack.

"The Emirates have the legal and moral right to defend their lands, population and sovereignty, and will exercise this right to defend themselves and prevent terrorist acts pursued by the Huthi group," he told US special envoy Hans Grundberg, according to the official WAM news agency.

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