A US citizen sentenced to 15 years of hard labour for what North Korea has described as hostile acts against the state has started life at a "special prison", state media said.
Few details were immediately available about the development for Kenneth Bae, the American arrested in November who Pyongyang accuses of trying to establish an anti-Pyongyang base in the North. Two South Korean experts on North Korean law said they did not know what a "special prison" was.
A North Korean academic, using information provided by the government, said earlier this week that Mr Bae had told his family in a phone call that he could not appeal against his April 30 sentence and that they should urge Washington to push for his freedom.
Washington has called for Mr Bae's release and human rights group Amnesty International has criticised his lack of access to a lawyer.
There has been no statement from Mr Bae. Pyongyang claims he confessed and did not want an attorney present during his sentencing.
The sentencing came during a period of tentative diplomatic moves following weeks of high tension and North Korean threats of nuclear and missile strikes on Washington and Seoul, and outside analysts have said Pyongyang may be using Mr Bae as bait to win diplomatic concessions in the stand-off over its nuclear weapons programme. North Korea denies such speculation.
Mr Bae is at least the sixth American detained in North Korea since 2009. The others were eventually deported or released without serving out their terms, some after trips to Pyongyang by prominent Americans, including former presidents Bill Clinton and Jimmy Carter.
There has been no sign yet of a high-profile American envoy to make a clemency mission to North Korea, which has eased a torrent of threats that followed greater UN sanctions over Pyongyang's nuclear test in February.
Young leader Kim Jong Un has the power to grant special pardons under the North's constitution.
Mr Bae is a Washington state resident described by friends as a tour operator based in the Chinese border city of Dalian, who travelled frequently to North Korea to feed orphans.