Hundreds of men swept up in the hunt for al-Qaida militants have disappeared into a secret network of prisons in southern Yemen where abuse is routine and torture extreme - including the grill," in which the victim is tied to a spit like a roast and spun in a circle of fire, an Associated Press investigation has found. Senior American defense officials acknowledged Wednesday that U.S. forces have been involved in interrogations of detainees in Yemen but denied any participation in or knowledge of human rights abuses. Interrogating detainees who have been abused could violate international law, which prohibits complicity in torture. The secret prisons are inside military bases, ports, an airport, private villas and even a nightclub. Some detainees have been flown to an Emirati base across the Red Sea in Eritrea, according to Yemen Interior Minister Hussein Arab and others. Several U.S. defense officials, speaking on condition of anonymity to discuss the topic, told AP that American forces do participate in interrogations of detainees at locations in Yemen, provide questions for others to ask, and receive transcripts of interrogations from Emirati allies. They said U.S. senior military leaders were aware of allegations of torture at the prisons in Yemen, looked into them, but were satisfied that there had not been any abuse when U.S. forces were present. Inside war-torn Yemen, however ... nearly 2,000 men have disappeared into the clandestine prisons, a number so high that it has triggered near-weekly protests.