ISTANBUL — The United Arab Emirates and allied security forces maintain a secret network of prisons in Yemen where dozens and perhaps hundreds of people are detained, routinely abused and in some cases severely tortured, according to separate reports released Thursday by Human Rights Watch and the Associated Press.

The investigation by the AP also found that forces from the United States, a close counterterrorism ally to the UAE, had participated in interrogations of prisoners in Yemen. American forces had been “yards” away from a facility where torture took place, one Yemeni security officer told the news agency.

The UAE is part of a Saudi-led military coalition fighting in Yemen against Houthi rebels and their allies, with the goal of restoring the government of ousted Yemeni President Abed Rabbo Mansour Hadi. The conflict has devastated Yemen, the Arab world’s most impoverished country, and killed more than 10,000 people, according to the United Nations.

The government of the UAE denied the existence of a clandestine prison network, telling the AP that “there are no secret detention centers, and no torture of prisoners is done during interrogations.”