North Korea in 2017 reportedly issued a $2 million bill to the U.S. for the hospital care of American Otto Warmbier, who was in a coma when he was returned to the U.S. and died without regaining consciousness.

The Washington Post reported Thursday that North Korea insisted that a U.S. official sign a pledge to pay the bill before returning Warmbier, an Ohio native who was arrested while visited Pyongyang.

Citing two people familiar with the situation, the Post reported that the U.S. envoy who retrieved Warmbier signed the pledge on instructions from President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE.

The Post says it's unclear if the Trump administration ultimately paid the bill.

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The White House reportedly declined to comment.

“We do not comment on hostage negotiations, which is why they have been so successful during this administration,” press secretary Sarah Huckabee Sarah Elizabeth SandersSarah Sanders on Trump's reported war dead criticism: 'Those comments didn't happen' Sarah Sanders memoir reportedly says Trump joked she should hook up with Kim Jong Un McEnany stamps her brand on White House press operation MORE Sanders told the newspaper in an email.

The Post reported Joseph Yun, the State Department envoy, was asked to sign the pledge when he went to North Korea to retrieve Warmbier.

Yun called then-Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE, who called Trump, according to the newspaper. Tillerson and Trump instructed Yun to sign the pledge, the Post said, according to two sources.

Yun, who retired last year, and the State Department also declined comment to the Post.

Warmbier's father, Fred Warmbier, told the news outlet he wasn't previously aware of the medical bill but said it sounded like a "ransom."

North Korea in 2016 sentenced Otto Warmbier to 15 years of hard labor, and the former University of Virginia student fell into a coma shortly thereafter.

Trump faced criticism earlier this year when he said he didn't think North Korean leader Kim Jong Un Kim Jong UnSatellite images indicate North Korea preparing for massive military parade South Korea warns of underwater missile test launch by North Korea Trump says he didn't share classified information following Woodward book MORE was responsible for Warmbier's death.

"Some really bad things happened to Otto. Some really bad things. [Kim] tells me that he didn't know about it, and I will take him at his word," Trump said.

Trump has twice met with Kim at summits. The most recent summit, held in February, ended without an agreement on denuclearization of the Korean Peninsula.

Updated at 12:30 p.m.