An US college student who emerged from prison in North Korea in a coma has severe brain damage but doctors do not know what caused it, a team treating him has said.
The doctors described Otto Warmbier, 22, as being in a state of "unresponsive wakefulness" but declined to discuss his outlook for improvement, saying such information would be kept confidential.
"He has spontaneous eye opening and blinking," said Dr Daniel Kanter, director of neurocritical care for the University of Cincinnati Health system.
"However, he shows no signs of understanding language, responding to verbal commands or awareness of his surroundings. He has not spoken."
Mr Warmbier is in stable condition at the UC Medical Centre, where he was taken immediately after his arrival in Ohio on Tuesday after more than 17 months in North Korean captivity.
The reclusive country accused the University of Virginia student of anti-state activities.
His father, Fred Warmbier, said the family was proud of their son, calling him "a fighter". He said the family is trying to keep him comfortable.
The elder Mr Warmbier said he did not believe North Korea's explanation that the coma resulted from botulism and a sleeping pill.
US doctors said they found no evidence of active botulism, a rare, serious illness caused by contaminated food or a dirty wound.
He said there was no reason for North Korea to keep his son's condition, apparently dating back to March 2016, a secret and to deny him top medical care.
Dr Kanter said the young man suffered "extensive loss of brain tissue in all regions of the brain".
Doctors said his injuries are consistent with respiratory arrest cutting off oxygen to the brain, but the are not certain what caused it.
They said an examination of the rest of Mr Warmbier's body found no evidence of fractures that might be evidence of severe beatings.
The family feels "relief that Otto is now home in the arms of those who love him and anger that he was so brutally treated for so long", his father said.
Otto Warmbier's father: President Trump called and wanted to find out about Otto, "he was very candid...it was a nice conversation." pic.twitter.com/izMIApxRYd— ABC News (@ABC) June 15, 2017
He spoke at Wyoming High School, where Mr Warmbier graduated in 2013. Blue-and-white ribbons were tied around trees and utility poles along the main road.
To honour his son, Fred Warmbier wore the same jacket Otto wore when North Korea presented him before the media on February 29 2016, at an event where he tearfully confessed that he tried to steal a propaganda banner.
He was last seen publicly that March, when he was sentenced for subversion to 15 years in prison with hard labour.
Fred Warmbier said that he does not know why North Korea released his son but the country does not do anything out of "the kindness of their hearts".
He called on the country to release three other Americans held there.
"There's no excuse for the way the North Koreans treated our son," he said.
In its first official comment since Mr Warmbier was returned home, North Korea said it released him for humanitarian reasons. The state-run Korean Central News Agency did not comment on his medical condition.
Mr Warmbier's father said he received "a very nice phone call" from President Donald Trump, who said Secretary of State Rex Tillerson worked hard to bring Otto home.
Mr Warmbier said the family was "extremely grateful for their efforts and concern".
He said he and his wife grew frustrated with the lack of word about their son from former president Barack Obama's administration, which they said instructed them to keep a low profile to avoid upsetting the North Koreans.
Asked whether he thought the previous administration could have done more, Fred Warmbier replied: "I think the results speak for themselves."
Mr Tillerson said on Tuesday that the State Department continues "to have discussions" with North Korea about the release of the other imprisoned Americans.