WASHINGTON (NYTIMES, REUTERS) - Otto Warmbier, the University of Virginia honours student who was released from a North Korean prison last week after spending 17 months in captivity and more than a year in a coma, died on Monday (June 19) at the Cincinnati hospital where he had been receiving treatment, his family said.

Warmbier's parents, Fred and Cindy, said in a statement that their son, 22, had "completed his journey home" and "was at peace" when he died.

"When Otto returned to Cincinnati late on June 13, he was unable to speak, unable to see and unable to react to verbal commands," the couple wrote. "He looked very uncomfortable - almost anguished. Although we would never hear his voice again, within a day, the countenance of his face changed - he was at peace. He was home, and we believe he could sense that."

The death was the end of a wrenching ordeal for the Warmbier family, and is likely to worsen the already tense relations between the United States and North Korea, which technically remain in a state of war dating to the armistice that halted the 1950-53 Korean War.

US President Donald Trump issued a terse statement condemning North Korea, which is still holding three Americans hostage.

"Otto's fate deepens my administration's determination to prevent such tragedies from befalling innocent people at the hands of regimes that do not respect the rule of law or basic human decency," the statement said.

"The United States once again condemns the brutality of the North Korean regime as we mourn its latest victim."

China, North Korea's main ally, lamented Warmbier's death. "It really is a tragedy. I hope that North Korea and the United States can properly handle the issue," Chinese Foreign Ministry spokesman Geng Shuang told a regular press briefing.

Asked if the death would have an impact on high-level US-China talks on Wednesday likely to focus on North Korea, Geng said China "remains committed to resolving the Korean Peninsula issue through dialogue and consultation".

Secretary of State Rex Tillerson said the United States holds North Korea accountable for Warmbier's "unjust imprisonment" and demanded the release of three other US citizens still held by Pyongyang - Korean-Americans Tony Kim, Kim Dong Chul and Kim Hak Song.

Offering condolence to the Warmbiers, South Korean President Moon Jae In urged Pyongyang to swiftly return the foreign detainees including six South Koreans.

Former Governor Bill Richardson of New Mexico, an expert on North Korea who has helped free other Americans held there, said in an interview on Monday that he had met with North Korean diplomats 20 times while Warmbier was being held, and that they had never hinted that anything was amiss with Warmbier's health.

Richardson called on the North to release the three other Americans it is holding, as well as a Canadian hostage, and to "disclose what happened to Otto, fully, to the international community."

Warmbier, a one-time high school soccer player and homecoming king with an adventuresome spirit, was travelling in China in December 2015 when he signed up for a five-day tour of North Korea with a Chinese company that advertised "budget travel to destinations your mother would rather you stayed away from."

The company, Young Pioneer Tours, said on Tuesday that it would no longer take Americans to North Korea because the "assessment of risk" was too high.

Warmbier was detained at the Pyongyang airport in early January 2016, charged with a "hostile act" against the country's authoritarian government and convicted less than two months later of trying to steal a propaganda poster, after he delivered a tearful, televised confession. His trial lasted one hour.

His parents, who live in the tiny city of Wyoming, Ohio, just outside Cincinnati, had heard nothing of him since his trial. Then, about two weeks ago, they received a call telling them their son was comatose. Days later, he was on a flight home.

At a news conference on Thursday morning, Fred Warmbier - wearing the same cream-coloured jacket Otto had worn during his trial - recalled kneeling to hug his son when he finally arrived home late last Tuesday.

"Otto is a fighter," Fred Warmbier said then, adding that he and his wife "firmly believe that he fought to stay alive through the worst that the North Koreans could put him through."

Otto Warmbier was taken immediately to the University of Cincinnati Medical Center, where doctors said that two MRI scans sent by the North Koreans indicated that Warmbier had suffered a catastrophic brain injury shortly after his conviction, most likely before April 2016.

The doctors said he had "extensive loss of brain tissue in all regions of his brain," most likely caused by cardiopulmonary arrest that cut off the blood supply to his brain.

But the doctors could not say what had caused the initial injury. While one senior American official said Warmbier had been singled out for particularly brutal beatings, doctors found no evidence of broken bones or other injuries consistent with physical abuse.

The North Koreans blamed a combination of botulism and sleeping pills for Warmbier's condition, but the doctors found no evidence of botulism.

Relations between the United States and the North have fallen to new lows in recent months over threats by North Korea's young leader, Kim Jong Un, to attack the United States with nuclear weapons.

Warmbier was one of more than a dozen Americans imprisoned in North Korea over the years, some for as long as two years, on accusations including illegal entry and sedition. But he is the first to have been sent home in a coma.

In their statement Monday, the Warmbiers said that they, like their son, were "at peace and at home," even as they lashed out at North Korea.

"Unfortunately," the statement said, "the awful, torturous mistreatment our son received at the hands of the North Koreans ensured that no other outcome was possible beyond the sad one we experienced today."