An American college student released by North Korea after 17 months in detention suffered a "severe neurological injury," a hospital spokeswoman said Thursday.
After returning home from North Korea, 22-year-old Otto Warmbier was immediately transported to the University of Cincinnati Medical Center hospital, where he is in stable condition.
Warch: Ohio Town Marks North Korean Captive's 'Bittersweet' Return
According to doctors, Warmbier suffered severe damage to all parts of his brain.
“He shows no signs of understanding language, responding to verbal commands, or awareness of his surroundings. He has not spoken, he has not engaged in any purposeful movements or behaviors," Dr. Daniel Kanter, who treated Warmbier, told a news conference Thursday.
Kanter and his colleagues added that they have no verifiable information about what happened to Warmbier before he left North Korea, and that, at his family's request, further information about his prognosis and prospects for improvement will remain confidential.
U.S. Secretary of State Rex Tillerson, attending a conference on Central America in Miami on Thursday, said, “We are glad he’s home rejoined with his family. We are not commenting on any of his health circumstances, it’s a private matter that’s up to him and the family. Nor are we going to comment on the circumstances of his condition and how he might have come to be in that condition. So I have nothing further to say on that. ”
Warmbier's parents said their son has been in a coma for more than a year, and they described his release as a medical evacuation.
At an earlier news conference Thursday, Fred Warmbier, Otto's father, said he does not believe what North Korea said was the cause of their son's condition.
"Even if you believe their explanation of botulism and a sleeping pill causing the coma, and we don't, there is no excuse for any civilized nation to have kept his condition secret and denied him top-notch medical care for so long," he said.
Fred Warmbier went on to say that the Trump administration has been more helpful in communicating with the family and facilitating the return of their son.
“The question is, do I think the past administration could have done more," Fred Warmbier said. "I think the results speak for themselves.”
WATCH: Fred Warmbier on son's condition after release
North Korea sentenced Warmbier, a student at the University of Virginia, to a 15-year prison term for attempting to steal a propaganda poster.
Fred and Cindy Warmbier said they were told their son was given a sleeping pill shortly after his trial last March, and that he never woke up.
State Department officials refused to comment on Warmbier’s health, citing department guidelines, but said the last time the U.S. had any access to Warmbier, through the Swedish Embassy, was March of last year.
VOA's State Department correspondent Nike Ching contributed to this report.