The self-proclaimed leader of a polygamist sect in Arizona who amassed more than 20 “wives,” including 10 “brides” under 18, was sentenced on Monday to 50 years in prison in connection with what prosecutors described as an interstate child sexual abuse ring, according to the U.S. Attorney’s Office in Arizona.

Federal prosecutors said that the man, Samuel R. Bateman, 48, of Colorado City, Ariz., led a group that victimized girls as young as 9.

Using his status as a self-declared prophet of the Fundamentalist Church of Jesus Christ of Latter-day Saints, Mr. Bateman forced his child “brides” to participate in sexual activities with him and with other adult men and women, prosecutors wrote in a sentencing memorandum.

Mr. Bateman was arrested in August 2022 when he was driving on a highway in Flagstaff, Ariz., pulling a box trailer with three young girls inside, along with a makeshift toilet, no air-conditioning, and a door that was not latched, prosecutors said.

In April, he agreed to plead guilty to two federal charges: conspiracy to commit transportation of a minor for criminal sexual activity, and conspiracy to commit kidnapping.

Under the plea agreement, he had faced a sentence of 20 to 50 years in federal prison. But prosecutors had argued that the “only appropriate sentence” would be 50 years.