Kenneth Bae, who was arrested in 2012, sentenced to 15 years hard labour, then freed after a secret mission to Pyongyang led by then-US intelligence chief James Clapper, said he was reasonably well treated in prison as he was a diplomatic bargaining chip.
"Everything depended on the US government's attitude," Korean-American Bae told South Korean broadcaster YTN in an interview broadcast live.
He said he had always thought it was "unimaginable" that a US citizen could die in a North Korean prison, and that he himself was never beaten or otherwise severely maltreated by the regime.
Bae said he had had to work long days in the fields doing manual labour, including planting beans and moving coal, a strenuous regime that caused him to lose 27 kilograms (60 pounds) during his period of detention.
But top Pyongyang officials, including a prosecutor, always made it clear they were going to trade him for diplomatic benefits, asking him "why the US government was so quiet" on his case and had not tried to free him immediately.
The prosecutor "told me the US had moved much quicker to secure the release of female journalists in 2009," Bae said, referring to Euna Lee and Laura Ling, who were released after a short period in North Korean detention following a visit from former US president Bill Clinton.
The prosecutor "even said that he thought I would be there until his retirement," Bae, whose two-year stint in detention is the longest period a US citizen has spent in a North Korean prison in recent years.
Warning from Pyongyang
"Since last year, I refrained from public activities out of concern that it could harm American and Canadian detainees in the North," Bae said in the interview.
But Warmbier's death had forced him to reconsider his position, he added.
"I came here today so that the death of the young man will not be futile but raise awareness about those detained in North Korea," he said.
Sentenced to 15 years of hard labour for stealing a political poster from a North Korean hotel while in the country as a tourist, 22-year-old Warmbier was medically evacuated from Pyongyang in a coma last week but died in the US Monday.
In the past North Korea has used the detention of US citizens to obtain high-profile visits from the likes of former US presidents Jimmy Carter and Clinton to secure their release.
Three US citizens are currently being held by North Korea, including two men who taught at a Pyongyang university funded by overseas Christian groups, and a Korean-American pastor who was accused of espionage for the South.
North Korea is also holding Korean Canadian pastor Hyeon Soo-Lim who was sentenced to life imprisonment with hard labour on sedition charges in December 2015.
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