"While I welcome the news of Mr Warmbier's release, I am very concerned about his condition, and the authorities have to provide a clear explanation about what made him slip into a coma", Tomas Ojea Quintana, the United Nations special rapporteur on human rights in the Democratic People's Republic of Korea (DPRK), said in a statement issued in Geneva.
Otto Warmbier has been in a coma for over a year and is receiving medical treatment at University of Cincinnati Medical Center.
A state department spokeswoman said in Washington, DC that Warmbier's release followed "quiet diplomacy", at US President Donald Trump's suggestion.
According to one of former President Barack Obama's advisers, the administration did what they can to secure the release of Warmbier, as they do for every American imprisoned overseas.
Father says Otto Warmbier "brutalized and terrorized" in N. Korea.
He was medically evacuated from North Korea and arrived in Cincinnati late Tuesday.
The other Americans held by Pyongyang are Kim Sang Duk and Kim Hak-song, academics who worked at the Pyongyang University of Science and Technology, and a businessman named Kim Dong Chul. "We hope that they will soon be able to return home", Nauert added.
Doctors said they can't speculate on what happened to Warmbier in North Korea, but that he likely suffered a respiratory arrest at some point in time, which could be the result of several causes.
His neurological condition was described by doctors 'as a state of unresponsive wakefulness'. "However, he shows no signs of understanding language, responding to verbal commands or awareness of his surroundings".More news: UK PM May said wants broader consensus on Brexit plan -lawmaker
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Doctors said they examined Warmbier's body and saw no evidence of fractures that might be evidence of severe beatings.
Warmbier is in stable condition at UC Medical Center, where he was taken Tuesday night after his arrival in Ohio.
Fred Warmbier echoed the message of U.S. officials, who have said Rodman played no role in the release. Experts said Otto was not responsive and could not move on his own when he was admitted to the hospital right after he landed on U.S. The reclusive country accused the University of Virginia student of anti-state activities. North Korea is a pariah regime.
Yun met with the North Korean ambassador to the U.N.in NY on June 6 and was told of Warmbier's medical status.
However, North Korean authorities said they had security footage from the Pyongyang hotel where Warmbier was staying showing him trying to steal a banner containing a political slogan that was hanging on a wall.
Doctors plan a news conference on campus later Thursday.
Speaking at a news conference on Thursday father Fred Warmber said he felt "relief that Otto is now home in arms of those who love him and anger that he was so brutally treated for so long".
Rodman, 56, did not disclose whether he had met with North Korean ruler Kim Jong-un, who he once called "a friend for life", only saying: "You'll find out".
Three more American citizens remain in North Korean custody.
Otto Warmbier's family say he's been in a coma for more than one year. "A really good trip", Rodman told reporters at Beijing's airport, Reuters reported.