Washington • North Korea insisted the U.S. agree to pay $2 million in medical costs in 2017 before it released detained American college student Otto Warmbier while he was in a coma, a former U.S. official said Thursday.

An envoy sent to North Korea to retrieve the 21-year-old student signed an agreement to pay the $2 million on instructions passed down from President Donald Trump, the former official told The Associated Press, speaking on condition of anonymity to discuss a sensitive diplomatic matter.

The Washington Post, citing two people familiar with the situation, first reported the demand and that the envoy signed the agreement.

The bill went to the Treasury Department, where it remained — unpaid — throughout 2017, the newspaper said. It is unclear whether the Trump administration later paid the bill, or whether it came up during preparations for Trump's two summits with North Korean leader Kim Jong Un.

White House press secretary Sarah Sanders said the administration does not comment on hostage negotiations. U.S. policy is to refuse to pay ransom for the release of Americans detained abroad.

While the majority of Americans detained by North Korea have been released in relatively good condition, Warmbier, a student at the University of Virginia, died in June last year shortly after he was flown home comatose after 17 months in captivity.

Warmbier was seized from a tour group while visiting North Korea in January 2016 and convicted on charges of trying to steal a propaganda poster and sentenced to 15 years of hard labor.

North Korea, which has denied accusations by relatives that it tortured Warmbier, has said he was provided "medical treatments and care with all sincerity."

Sen. Rob Portman, R-Ohio, said the United States doesn't owe North Korea anything.

"Otto Warmbier was mistreated by North Korea in so many ways, including his wrongful conviction and harsh sentence, and the fact that for 16 months they refused to tell his family or our country about his dire condition they caused," Portman said. "No, the United States owes them nothing. They owe the Warmbier family everything."

Parents Fred and Cindy Warmbier are from suburban Cincinnati, Ohio.

Robert Lewis, a spokesman for the law firm that filed suit against North Korea on behalf of the Warmbier family, declined comment.

Yun told CNN on Thursday that he could not discuss details of his diplomatic discussions. He said his orders from Trump were to "do whatever" he could to get Warmbier back.

Asked if it would be unusual for the U.S. to pay medical costs of detainees, Yun said: "There was some expectation the North Koreans might raise hospital costs." He said that in past instances not involving Warmbier "some money could have been handed over, yes."

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