The United Arab Emirates is facilitating torture, including sexual violence, beatings and electric shocks, in secretive prisons in southern Yemen, a new report from Amnesty International has alleged.

Men suspected of belonging to either al-Qaeda or Isis have been forcibly disappeared in detention centres either run by UAE forces or Yemeni militias under their control since the country’s civil war broke out in 2015, the rights watchdog said in a new report published on Thursday.

Amnesty investigated the fate of 51 men swept up in the Arab coalition’s hunt for extremists since March 2016. Families who have formed protest groups to discover the whereabouts of loved ones say hundreds of men in total have been disappeared.

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The findings reinforce recent reports from the Associated Press and local protest groups into alleged disappearances and abuses – including that several activists, journalists and members of the Yemeni Muslim Brotherhood have been detained after terror-related accusations.

The collected evidence amounts to war crimes which should be immediately addressed in an international investigation, Amnesty says.

Current and former detainees described widespread horrific treatment such as the use of electric shocks, severe beatings, anal rape with metal poles and being forced to live in cramped conditions.

“I saw things I do not want to see again. In that place, you do not even see the sun… Then one day, they released me at night, they said they had me confused with someone else… ‘It was a mistaken identity, sorry’. It was as if they had done nothing after all the suffering I endured from electric shocks,” said one former detainee at a facility in Aden.

“The families of these detainees find themselves in an endless nightmare where their loved ones have been forcibly disappeared by UAE-backed forces,” Amnesty’s crisis response director Tirana Hassan said in a statement.

“When they demand to know where their loved ones are held, or if they are even still alive, their requests are met with silence or intimidation.”

The UAE has publicly denied all allegations of holding or abusing detainees.

“The UAE does not manage or run prisons in Yemen,” the government-run National Media Council said in a statement on Thursday.

“[We believe] that these reports are politically motivated to undermine its efforts as part of the Arab coalition to support the Yemeni government.”

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The Emirates and Saudi Arabia are the exiled Yemeni government’s main allies in its fight to regain control of the country from Houthi rebels, who are supported by Iran.

Since last year the UAE has also backed a militia known as the Southern Transitional Council, which seeks renewed independence for southern Yemen, and funded and trained various other local security forces which bypass the central Yemeni government.

“The UAE, operating in shadowy conditions in southern Yemen, appears to have created a parallel security structure outside the law, where egregious violations continue to go unchecked,” said Ms Hassan.

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The Arab coalition is backed by several western partners, including the UK and US, which also sell Abu Dhabi and Riyadh weapons Amnesty says have caused unnecessary civilian deaths in the brutal three-year-old war.

After the publication of a new AP report into UAE-run prisons in Yemen last month, several missing people have been released.