The Warmbier family confirmed on Monday that he had died.
US State Department spokeswoman Heather Nauert said earlier the US would hold North Korea accountable for Warmbier's "unjust imprisonment" and called for the release of three other Americans detained in the country.
Warmbier was arrested and imprisoned in North Korea during President Barack Obama's time in office, though North Korea only informed the USA of Warmbier's medical condition earlier this month.
The U.S. government strongly warns Americans against traveling to North Korea, but doesn't prohibit it, despite other sanctions targeting the country.
Last week North Korea made a "humanitarian" gesture, releasing US college student Otto Warmbier from custody, 17 months into his 15 year hard labor sentence for the crime of allegedly trying to steal a propaganda poster.
The 22-year-old was medically evacuated last week and was being treated at the University of Cincinnati Medical Center when he breathed his last on Monday.
The Warmbier family's "objection to an autopsy was honored", the office said, and only an external examination was performed.
The statement did not explicitly mention a cause of death but did say that "the very bad torturous mistreatment our son received at the hands of the North Koreans ensured that no other outcome was possible".
The death this week of an American university student held prisoner for 17 months by North Korea left OH municipal worker Jeffrey Fowle shaken.
While visiting the hermit state in 2016, Warmbier was jailed for trying to steal a propaganda poster.
Doctors in Cincinnati say he had suffered a severe injury impacting all regions of his brain. Though Kanter said that Warmbier was stable at the time and breathing on his own, "he has not spoken".
"This is something we may be able to discuss at a later stage when the threat has become even more urgent", he said, adding that the North Korea nuclear missile threat was a matter of life or death for the South Koreans who live next door.
"We must not show them a weakness or a gap in our united front that they would exploit for their own purposes", said the diplomat, who requested anonymity.
Last month, California Democratic Rep. Adam Schiff and his Republican colleague Rep. Joe Wilson of SC introduced the North Korea Travel Control Act.
Shi Yinhong, a professor of worldwide relations at Renmin University in Beijing, said that China would not punish North Korea over a human rights issue. Almost all Americans who have gone to North Korea have left without incident. A senior administration official, speaking on condition of anonymity, said the United States had limited options to rein in North Korea without Chinese assistance.
Warmbier was on a tourist trip when he was arrested and sentenced in March last year to 15 years hard labour for stealing a political poster from a North Korean hotel, a punishment U.S. officials decried as out of proportion to his alleged crime. They did not cite a specific cause of death.
Warmbier was released on June 13 in a state of coma after Joseph Yun, the State Department's special envoy on North Korea, paid a visit to Pyongyang and demanded his release.