WASHINGTON (AP) — Lawyers for an American believed to be held by the Taliban for nearly two years are asking a United Nations human rights investigator to intervene, citing what they say is cruel and inhumane treatment.

Ryan Corbett was abducted Aug. 10, 2022, after returning to Afghanistan, where he and his family had been living at the time of the collapse of the U.S.-based government there a year earlier. He arrived on a valid 12-month visa to pay and train staff as part of a business venture he led aimed at promoting Afghanistan’s private sector through consulting services and lending.

Corbett has since been shuttled between multiple prisons, though his lawyers say he has not been seen since last December by anyone other than the people with whom he was detained.

In a petition sent Thursday, lawyers for Corbett say that he’s been threatened with physical violence and torture and has been malnourished and deprived of medical care. He’s been held in solitary confinement, including in a basement cell with almost no sunlight and exercise, and his physical and mental health have significantly deteriorated, the lawyers say.