Matthew Miller, the American held in North Korea since April for "hostile acts", began a six-year hard labor sentence on Thursday that he said involved farm work and isolation, media reports said.
Miller, 25, said in an interview with the Associated Press he had written to U.S. First Lady Michelle Obama, Secretary of State John Kerry and his predecessor Hillary Clinton asking for help.
"Prison life is eight hours of work per day," Miller, dressed in grey prison clothes and a hat, said in the video interview. "Mostly it's been agriculture, like in the dirt, digging around. Other than that, it's isolation, no contact with anyone."
CNN also reported that a North Korean government official released a photo of Miller, taken on Wednesday, his head shaved and in grey prison clothes with the number 107 on his chest and staring away from the camera.
North Korea's state media said on Saturday that he pretended to have secret U.S. information and was deliberately arrested in a bid to become famous and meet Kenneth Bae, another American detainee in a North Korean prison.
Reuters reported earlier that Miller spent months in South Korea pretending to be an Englishman named "Preston Somerset" and invested time and money hiring artists to help create his own anime adaption of Alice in Wonderland, the Lewis Carroll fantasy with which he seemed fascinated.
Bae, a missionary of Korean descent, is serving a 15-year hard labor sentence after being convicted of crimes against the state last year.
Bae has also appeared before cameras appealing to the U.S. government for help to secure his release. He said he was being held in a special correctional facility.
A third American, Jeffrey Fowle, was arrested for leaving a copy of the Bible in the toilet of a sailor's club in the port city of Chongjin and is currently awaiting trial.
The United States has said Pyongyang is using its citizens as "pawns" to win a high-level visit from Washington.
Former U.S. presidents Jimmy Carter and Bill Clinton have both made trips to the North to secure the release of Americans held in the secretive state.