Otto Warmbier, a student at the University of Virginia, was arrested for removing a political banner from a wall in a North Korean hotel during a visit.
North Korea has released 22-year-old American student Otto Warmbier from a 15-year sentence of hard labour, officials said Tuesday, as former US basketball star Dennis Rodman arrived in Pyongyang.
Secretary of State Rex Tillerson confirmed the release, and said Washington remains in talks with the isolated regime "regarding three other US citizens reported detained."
Officials could not immediately confirm US media reports that Warmbier has fallen into a coma during his incarceration.
"We have no comment on Mr Warmbier's condition, out of respect for him and his family," Tillerson told US senators at the start of a hearing into his budget.
However, Bill Richardson, a veteran former diplomat and politician who has played a role in past negotiations with North Korea, said: "Otto has been in a coma for over a year now and urgently needs proper medical care in the United States." He made the comments after speaking to Warmbier's parents.
The family said they were told by North Korean officials, through contacts with American envoys, that Warmbier fell ill from botulism sometime after his March 2016 trial and lapsed into a coma after taking a sleeping pill, the Washington Post reported.
"In no uncertain terms North Korea must explain the causes of his coma," Richardson, whose Center for Global Engagement had directly sought Warmbier's release with the North Korean government, said in a statement.
Warmbier, a student at the University of Virginia, was arrested for removing a political banner from a wall in a North Korean hotel during a visit.
He was detained at the airport as he was leaving the country with a tour group in January 2016.
The United States has accused the North of using Warmbier as a political pawn and condemned the sentence as far out of proportion to his alleged crime.