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An American man recently sentenced by North Korea to six years of hard labor says he is working eight hours a day digging in fields and being kept in isolation, but that so far his health isn't deteriorating.

Under close guard and with only enough time to respond to one question, 24-year-old Matthew Miller spoke briefly to an Associated Press Television News journalist at a Pyongyang hotel, where he had been brought to make a phone call to his family. It was his first appearance since he was convicted Sept. 14 of entering the country illegally to commit espionage.

"Prison life is eight hours of work per day. Mostly it's been agriculture, like in the dirt, digging around," Miller said when asked if he was in prison and if so what conditions were like.

"Other than that, it's isolation, no contact with anyone. But I have been in good health, and no sickness or no hurts," he said, showing little emotion.

Wearing a prison-style gray uniform and cap, Miller was filmed sitting down at a phone booth at the hotel and pressing the buttons on a phone while a North Korean guard stood behind him. Officials said Miller spoke to his father, but the APTN journalist was not allowed to hear the conversation. Miller does not have routine access to phone calls home.

The Bakersfield, California, native showed several letters he had written pleading for help from influential Americans, including first lady Michelle Obama, U.S. Secretary of State John Kerry and former U.S. Secretary of State Hillary Clinton.

At Miller's 90-minute trial, North Korea's Supreme Court said he tore up his tourist visa at Pyongyang's airport upon arrival on April 10 and admitted to having the "wild ambition" of experiencing prison life so that he could secretly investigate North Korea's human rights situation.

Miller is one of three Americans detained in North Korea. Jeffrey Fowle, who was arrested in May for leaving a Bible at a sailor's club, is expected to be tried in court soon. Kenneth Bae was sentenced in 2013 to 15 years of hard labor.

Last week, Robert King, the U.S. special envoy for North Korean human rights issues, said Pyongyang has not accepted American offers to send a high-level envoy to seek release of the three men. King said that freeing the detainees could provide a diplomatic opening in ties between the two countries, but that Washington would not give into attempts to "extort" political gain from the detentions.

King would not specify whom the Obama administration was willing to send. But Scott Snyder, senior fellow for Korea Studies at the Council on Foreign Relations think tank, said he was told by the administration that it has offered in recent weeks to send Glyn Davies, who leads U.S. diplomacy on North Korea's nuclear weapons program, and Pyongyang has not responded favorably.

In 2009, North Korea detained two American journalists, Laura Ling and Euna Lee, who were later freed after former U.S. President Bill Clinton visited Pyongyang. In 2011, former President Jimmy Carter visited North Korea to win the release of imprisoned American Aijalon Gomes, who had been sentenced to eight years of hard labor for crossing illegally into the North from China.