Human Rights Watch (HRW) has called on the United Arab Emirates (UAE) to stop mistreatment of prisoners in informal jails they oversee in Yemen that has led the detainees to go on hunger strike.

The rights group issued a report on Thursday, citing prisoners’ family members as saying the hunger strike started on October 21 at the Bir Ahmed military camp in Aden.

“The UAE and their Yemeni proxies should stop denying responsibility for mistreatment and investigate and act on the complaints,” said Sarah Leah Whitson, the group’s Middle East director.

UAE-backed militants have reportedly kidnapped and tortured hundreds of people in southern Yemen in recent months.

According to an investigation, the militants have brought the people to a secret prison compound in southern Yemen, where they were tortured.

Since 2015, Saudi-led coalition including the UAE has launched a military campaign against Yemen, which started in March 2015, to restore the country’s former Riyadh-friendly government.

The military campaign has so far killed more than 14,000 Yemeni civilians. As a result of the war, much of Yemen’s infrastructure including hospitals, schools and factories, has been ravaged.

Nearly seven million Yemenis face famine and some 16 million do not have proper access to water or sanitation as a result of the military campaign.