"There had not been any previous detainment in North Korea that has ended with such tragic finality", the company said, adding that Warmbier's death had made it "reconsider" its position on accepting American tourists.
Warmbier was arrested by North Korean authorities in January 2016 for attempting to steal a propaganda poster from a restricted area within his hotel.
On Monday, President Donald Trump offered his condolences to the family of Otto Warmbier, who died Monday after being held for more than 17 months by North Korea. Unfortunately, the very bad 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. "He looked very uncomfortable - nearly anguished", they said.
"Although we would never hear his voice again, within a day the countenance of his face changed - he was at peace", the statement continued.
Speaking during a White House event, he added: "It's a brutal regime and we'll be able to handle it". Secretary of State Rex Tillerson said the USA holds North Korea accountable for Warmbier's "unjust imprisonment" and demanded the release of three other American citizens still in detention.
The death is likely to exacerbate relations between the United States and North Korea, whose leader, Kim Jong-un, has threatened to attack the USA with nuclear weapons in recent months.
But a team of doctors assessing him in Cincinnati said they had found "no sign of botulism" in the student.
But the young man who landed in Cincinnati and was immediately taken to a hospital isn't the same person who left a year and a half ago on a trip to explore the secretive country.
In a 2016 piece on the Vibe.com website, Johnson is quoted as saying he launched the company after finding an low-cost way to get into Hong Kong and getting drunk with a North Korean "in charge of stuff".
He was sentenced to 15 years of hard labour in March 2016 for trying to steal a political banner, and was medically evacuated to OH last week.
They said Warmbier's severe brain injury was most likely - given his young age - to have been caused by cardiopulmonary arrest cutting the blood supply to the brain.
Young Pioneer Tours, the travel company that took Warmbier to North Korea, has said it will no longer take U.S. citizens into the country because "the risk is too high".
North Korea said it had released Mr Warmbier "on humanitarian grounds".
But instead of graduating in May with the rest of his class, Warmbier was still in North Korea. The US government accuses North Korea of using such detainees as political pawns. The tours offer themes ranging from politics to biking along the DMZ demilitarized zone between North and South Korea to scuba diving.
At the time, he declined to discuss Warmbier, except to say, "If I bring guests that are respectful, willing to listen, willing to interact with people, North Koreans will see that we are normal people as well".