American Matthew Miller began his six-year sentence in North Korea Thursday and described the “isolation” in which he is being held.

“Prison life is eight hours of work per day. Mostly it's been agriculture, like in the dirt, digging around. Other than that, it's isolation, no contact with anyone,” Miller told the Associated Press in an interview that was reportedly heavily monitored by North Korean minders.

The video shows Miller, in a prison uniform, being allowed to make a phone call to his family, before he officially begins serving his sentence. Miller reportedly also handed journalists letters that he had written to high-ranking U.S. officials, including Secretary of State John Kerry, pleading for them to intervene in his case.

Miller was sentenced on Sept. 14 for "acts hostile to the DPRK." North Korea's state news agency, KCNA, described him as "rudely behaved," saying he was sent to infiltrate a prison as part of an American campaign against North Korea, according to a report from CNN. “He perpetrated the above-said acts in the hope of becoming a world famous guy and the second Snowden through intentional hooliganism," the agency said.

Miller was detained in the country in April. Miller told the Associated Press that he tore up his North Korean tourist visa and asked for asylum when he arrived in Pyongyang.

Two other Americans, Jeffrey Fowle, 56, and Kenneth Bae, 44, are currently being held in North Korea. Bae, a Christian missionary, is serving a 15-year sentence for crimes the North Korean government said amounted to an attempt to overthrow the state.

Fowle has yet to be tried, but is accused of leaving a Bible in a hotel room. Proselytizing is forbidden in North Korea, and in recent months, the country has been involved in a crackdown against missionaries.

Miller's plea comes in the wake of Kerry's call Tuesday for North Korea to shut down its "evil system" of prison camps, according to a report from the AP. Kerry has said that abuses alleged to have taken place in the camps, outlined in a U.N. report released earlier this year, "have no place in the 21st century."