An American college student who was recently released from North Korea has suffered severe brain damage, his doctors said Thursday, adding to growing calls in the USA for a travel ban to the reclusive nation amid souring public sentiment and safety concerns.

"He announced that Warmbier "[showed] no sign of understanding language, responding to verbal commands or [being aware of] his surroundings".

Former NBA star Dennis Rodman on Saturday concluded his five-day visit to North Korea.

Although doctors had no information about the type of medical treatment Warmbier received while in North Korea, they did receive MRI images from North Korea dated April 2016, Kanter said.

"He has not spoken", Kanter added.

Doctors indicate that Otto Warmbier's current state is consistent with the aftermath of cardiopulmonary arrest that deprives the brain of blood.

Rodman has been visiting North Korea since Tuesday, his latest trip to the isolated state. His family was unaware of his condition until he was released.

North Korean authorities claimed Warmbier's coma was caused by botulism and a sleeping pill, an explanation his doctors dismissed on Thursday.

Fred Warmbier also said the family does not believe North Korea's story that "botulism and sleeping pill" caused his coma. North Korea is a pariah regime.

"It appears to be exotic to go to the country, but it's all staged", he says.

Ned Price said that the administration was able to secure the release of 10 other Americans who are imprisoned in North Korea.

They said his prognosis remains confidential. "No other family should have to endure what the Warmbiers have".

North Korea said Warmbier had been released on humanitarian grounds after he was sentenced to 15 years hard labour for trying to steal a propaganda sign.

Another tour company, Koryo Tours, asserts that North Korea "is probably one of the safest countries in the world for a tourist", claiming on its site that past detainees committed crimes. The said material was used during the court trial where he was found guilty of committing "hostile acts" while on tour.

North Korea officials have stated that Warmbier fell into a coma shortly after his incarceration in March, 2016.

His parents learned of their son's condition - what North Korea called a coma - only last week, they said in a statement.

North Korea reportedly told a USA official that Otto contracted botulism while detained and slipped intothe coma after taking a sleeping pill.

They say his brain shows significant tissue damage, but a cause for his disease is unknown. He said Warmbier was breathing on his own.

The hermit state freed Otto Warmbier on Tuesday after about 17 months in custody.

Richardson, a former New Mexico governor and congressman who visited North Korea in the 1990s and sought the release of detained Americans, told Reuters he made the proposal in a letter to the North Korean mission to the United Nations.

Warmbier also revealed he and his wife were told by Obama administration officials not to hang ribbons representing Otto's captivity in their community because it would have been offensive to North Korean officials. A Young Pioneer Tours official told a news site that focuses on the region that only one person - Otto Warmbier - has ever been arrested among the 8,000-plus worldwide travelers who have taken part in the company's tours.