Warmbier's release came during a visit to North Korea by former National Basketball Association star Dennis Rodman, one of few people to have met both North Korean leader Kim Jong Un and President Donald Trump.
Phil Robertson, deputy Asia director at Human Rights Watch, said, "It's clear that Pyongyang has committed a grave injustice against Otto and his family, and the news that he may be returning with a serious medical problem raises concerns about what happened to him in North Korean custody".
It is not immediately possible to determine whether Mr. Warmbier's condition is due to events as described by the North Korean government.
Rodman - a former contestant on Trump's Celebrity Apprentice television show - has travelled to the reclusive state four times since 2013 as part of a quixotic mission to broker a detente deal between the U.S. and North Korea.
Analyst Daniel Pinkston, a lecturer at Troy University, said he did not believe that Rodman was going as a back-channel emissary from Trump despite United States media speculation.
Any visit to North Korea by a high-profile American is a political minefield.
But on his final night in Pyongyang - New Year's Eve - he apparently went to a staff-only floor of his hotel and attempted to take down a large propaganda sign lauding the regime.
The North Korean court held that Warmbier had committed a crime "pursuant to the USA government's hostile policy toward (the North), in a bid to impair the unity of its people after entering it as a tourist". His current visit has already been roundly criticized by some for its timing, during high tensions between the USA and North Korea over its weapons programs and recent missile launches. Officials involved in negotiations to free Warmbier and another American citizen who is being detained were told they were being treated as prisoners of war.
After the Swedish diplomats met with the detained Americans, the North Koreans urgently asked to have a meeting with the U.S.in NY.
But in Pyongyang, the Swedes were allowed to see only one detainee, and it wasn't Warmbier.
When asked if he would bring up the cases of Warmbier and three other Americans detained in North Korea, Rodman told reporters, "that's not my goal right now". "This is him freelancing", the official told Reuters.
If it were, there might be pressure on President Trump to take action against Kim Jong-un's regime, he says.
EPAThe University of Virginia student was accused of trying to steal a propaganda flag by North Korea
The young undergraduate honors student was forced the next month, at a staged news conference, to admit to a "very severe and pre-planned crime", saying that the "aim of my task was to harm the motivation and work ethic of the Korean people".
This combination of file photos shows former NBA basketball star Dennis Rodman in Pyongyang, North Korea on December 20, 2013, left, and North Korean leader Kim Jong Un in Pyongyang on April 15, 2017. The official referred to them as "hostages".
Rodman, one of the few people to know both of the nuclear-armed leaders, sported a black T-shirt advertising a marijuana cybercurrency as he talked to reporters briefly before his flight from Beijing to the North Korean capital. A department of state spokeswoman said the former basketball player had nothing to do with Warmbier's release. Yun and two physicians flew to Pyongyang and visited Warmbier Monday.
Despite the increasingly hostile US-North Korean relationship, the Warmbiers said they were encouraged by US President Donald Trump's willingness to improve relations with North Korea. Pritish Tosh, an infectious diseases physician, told the Washington Post that in some very specific instances, patients suffering from botulism may be placed in medically induced comas while being connected to a ventilator to facilitate their care, though it is now unclear if that's what happened to Warmbier. USA officials did not confirm those details.
Tillerson did not elaborate on Warmbier's current health condition, and said he would not be offering additional comment out of respect for the family's privacy. The North Koreans "were informed that the airplane would land".
Regardless of how Warmbier's coma began, his prognosis could be grim, given that he has been in a state of unconsciousness for approximately a year. "He doesn't deserve this", Fred Warmbier told the Enquirer last month in an interview.
"In no uncertain terms North Korea must explain the causes of his coma", veteran former diplomat Bill Richardson said in a statement after speaking to Warmbier's parents.
During a government-arranged news conference in Pyongyang, which was held a month before the ruling was handed down, a tearful Warmbier pleaded for his release, saying he stole the banner because a member of his church offered to buy him a used vehicle in exchange.
It is good to have him returned to his family and to better medical care.
"Otto's detainment and sentence was unnecessary and appalling, and North Korea should be universally condemned for its abhorrent behavior".
Three other Americans remain in North Korean jails.
South Korea-born Kim Dong Chul, now aged around 63 or 64, was arrested in October 2015 on charges of espionage and other undisclosed crimes. With concern mounting over Warmbier's deteriorating condition since the State Department learned of it in early June, a delegation arrived in Pyongyang on June 12 that included a State Department representative and a medical team.