DOCTORS treating the US uni student released by North Korea say he has “extensive loss of brain tissue” and is in a “state of unresponsive wakefulness”.

Dr Daniel Kanter, professor of neurology and director of the Neurocritical Care Program at the University of Cincinnati Medical Centre, said Otto Warmbier’s condition is best described as “unresponsive wakefulness.”

“He shows no signs of understanding language or responding to verbal commands,” he said.

Otto, 22, a University of Virginia student, was serving a 15-year sentence for stealing a political poster from a North Korea hotel.

When North Korea released him under what it said were “humanitarian grounds”, officials said he had contracted botulism.

However, doctors said there were no signs of botulism, a condition often associated with contaminated food, which can cause the nerves not to function properly and basically, leads to paralysis in some muscles.

The most important diagnostic test conducted, doctors said, showed that Otto had extensive loss of brain tissue in all regions of the brain.

His father, Fred Warmbier, said his son was “brutalised” by his captors.

“There’s no excuse for the way the North Koreans treated our son and no excuse for the way they have treated so many others,” Fred Warmbier told a news conference in the family’s home city of Cincinnati, Ohio.

“I call on them to release the other Americans being held,” he urged.

Fred and Cindy Warmbier have said their son was “terrorised and brutalised” by Kim Jong-Un’s regime.

According to Kelly Martin, spokeswoman for the UC Health University of Cincinnati medial center, “Otto is in stable condition but has suffered a severe neurological injury.”

Mr Warmbier earlier told Fox News from his Ohio home that his son, Otto, “is not in great shape right now.”

Mr Warmbier, said he does not believe North Korea’s explanation that the coma resulted from botulism and a sleeping pill. He said there was no reason for North Korea to keep his son’s condition a secret and deny him top medical care.

The 22-year-old University of Virginia student was medically evacuated from North Korea and flown to Cincinnati late on Tuesday. He was then taken by ambulance to a hospital.

Mr Warmbier said he does not know exactly what happened to his son during his detention.

Residents of the northern Cincinnati suburb tied blue-and-white ribbons, the school colours, to trees near the family home. Joy at his release was mixed with concern after his parents said they were told he had been in the coma for over a year.

Former New Mexico Governor Bill Richardson, a former US ambassador to the United Nations, said there should be an investigation into what happened to Otto Warmbier leading to this “tragic situation.”

Gov. Richardson, a Democrat, credited the Department of State with securing Otto Warmbier’s return from North Korea without any preconditions but said a forceful response from the US government would be required “if it’s determined that there was a cover-up and Otto’s condition was not disclosed and he didn’t get proper treatment.”

City councilwoman Jenni McCauley said the tight-knit community was “thrilled” to have Otto Warmbier back.

“Even though they’re saddened by his condition, they’re just glad for the family that he is home,” Mr McCauley said. “For any parent, this is their worst nightmare. ... We’re hoping that he will be OK.”

She called him “a fabulous young man” who was known as intelligent, personable and well-liked in school and in the community.

Ellie Boettcher, a 14-year-old rising freshman at Wyoming High, where Otto Warmbier’s sister will be a sophomore, said students were elated.

“We’re just really glad that he’s able to come back,” Ellie said. “Nothing really bad ever happens in Wyoming. It’s kind of like a bubble. So it’s really tragic. But luckily he is back, and I believe he will make a full recovery.”

Otto Warmbier was serving a 15-year prison term with hard labour in North Korea.

He had tearfully confessed to trying to steal a propaganda banner while visiting.

He was released on Tuesday, more than 17 months after being detained.

Such detentions in the totalitarian nation have added to tensions between Washington and Pyongyang.

Three Americans remain in custody.

The US government accuses North Korea of using such detainees as political pawns.

North Korea accuses Washington and South Korea of sending spies to overthrow its government.

Secretary of State Rex Tillerson said on Tuesday that his department was continuing “to have discussions” with North Korea about the release of the other three imprisoned American citizens.