Southern Yemeni prisons should be investigated for "war crimes", according to Amnesty International.
Human rights violations in a string of Yemeni prisons run by the United Arab Emirates could amount to war crimes, Amnesty International said Thursday.
It called for investigations by the UAE and allies including the United States into a network of unofficial prisons across southern Yemen where it said "egregious violations" have been committed, including enforced disappearances and torture.
"Ultimately these violations, which are taking place in the context of Yemen's armed conflict, should be investigated as war crimes," said Tirana Hassan, Amnesty's crisis response director.
"The UAE's counter-terrorism partners, including the USA, must also take a stand against allegations of torture, including by investigating the role of US personnel in detention-related abuses in Yemen, and by refusing to use information that was likely obtained through torture or other ill-treatment."
The UAE has denied involvement in prisons across southern Yemen.
The Gulf state has played a key role in a Saudi-led military intervention since 2015 to bolster Yemen's President Abedrabbo Mansour Hadi against Iran-backed Huthi rebels.
Both loyalist and rebel forces stand accused of failing to protect civilians in a war that has killed nearly 10,000 people, 2,200 of them children, and pushed the country to the brink of famine.
Amnesty International said it had investigated 51 cases of enforced disappearance at the hands of UAE-backed forces between March 2016 and May 2018.
Nineteen of the men remain missing, it said.
Amnesty said it had collected testimonies from released detainees and relatives of the missing across Yemen.
One former detainee told Amnesty that "UAE soldiers at a coalition base in Aden repeatedly inserted an object into his anus until he bled" and that he was "kept in a hole in the ground with only his head above the surface and left to defecate and urinate on himself in that position".
Since joining the Yemen war in 2015, the UAE has trained, equipped and funded Yemeni security forces known as the Security Belt and Elite Forces. The UAE has also "built alliances" with Yemeni security officials, bypassing the government, according to Amnesty.
This week the UAE minister for international cooperation, Reem al-Hashimi, met with Yemen's president and interior minister, who "insisted on the need to close the prisons and place them under judicial control", according to Yemeni state media.