American Marconi Wireless News - Coalition denies Yemen prison air strike that killed 70

Claims the military coalition ordered the raid, which reduced buildings to rubble and left rescuers scrabbling for survivors with their bare hands, were "groundless", the alliance said.

The attack, which coincided with a coalition strike on Hodeida that killed three children and knocked out the impoverished country's internet, was condemned by the United Nations secretary-general.

But "these claims adopted by the militia are baseless and unfounded", said coalition spokesperson Turki al-Malki, referring to the Iran-backed Huthi insurgents.

The latest violence in Yemen's intractable, seven-year war came after the Huthis claimed their first deadly attack on Abu Dhabi, capital of coalition partner the United Arab Emirates, on Monday.

This week has witnessed a dramatic upswing in the conflict that has already killed tens of thousands of people and displaced millions, creating what the UN calls the world's worst humanitarian crisis.

The rebels seized the capital Sanaa in 2014, prompting the Saudi-led intervention -- supported by the US, France and Britain -- in March 2015. It was intended to last just a few weeks.

The internet blackout, which went into its second day on Saturday according to web monitor NetBlocks, complicated rescue work and media reporting as information slowed to a trickle.

Unverified footage released by the Huthis revealed gruesome scenes at the bombed-out prison facility as rescue workers scrabbled to dig out bodies and mangled corpses were placed in piles.

- 'Horrific act of violence' -

Eight aid agencies operating in Yemen said in a joint statement that the prison in Saada, the rebels' home base, was used as a holding centre for migrants, who made up many of the casualties.

They said they were "horrified by the news that more than 70 people, including migrants, women and children, have been killed... in a blatant disregard for civilian lives".

Hospitals were overwhelmed as hundreds of casualties flooded in, aid workers said.

"It is impossible to know how many people have been killed. It seems to have been a horrific act of violence," said Ahmed Mahat, Doctors Without Borders' head of mission in Yemen.

The strikes came after the Huthis took the seven-year war into a new phase by claiming the drone and missile attack on Abu Dhabi that killed three people on Monday.

The UAE threatened reprisals after the attack, which was the first deadly assault it has acknowledged inside its borders that was claimed by the Huthis.

Meeting on Friday, the UN Security Council unanimously condemned the "heinous terrorist attacks" on Abu Dhabi, but the council's Norwegian presidency also denounced the strikes on Yemen.

In a later statement, the UN chief Antonio Guterres "reminds all parties that attacks directed against civilians and civilian infrastructure are prohibited by international humanitarian law".

US Secretary of State Antony Blinken called for "all parties to the conflict to de-escalate" and "abide by their obligations under international humanitarian law".

However, the Huthis warned foreign companies to leave the "unsafe" UAE, a veiled threat of revenge attacks after Friday's strikes.

"We advise the foreign companies in Emirates to leave because they invest in an unsafe country and the rulers of this country continue in their aggression against Yemen," tweeted military spokesperson Yahya Saree.

A.Mahlangu--AMWN