North Korea claimed Friday that it doesn't know why American college student Otto Warmbier's health was so poor that after months of imprisonment he ended up dying — and said it even revived him after his "heart was nearly stopped."

"The fact that Warmbier died suddenly in less than a week just after his return to the U.S. in his normal state of health indicators is a mystery to us as well," a North Korean foreign ministry spokesman was quoted as saying by the state-run Korean Central News Agency.

The spokesman also blamed the Obama administration for failing to act sooner to help Warmbier, saying the 22-year-old University of Virginia undergrad was "a victim of policy of 'strategic patience.'" The Obama administration, the spokesman said, never asked for his release.

Warmbier died Monday after his June 13 return to his home state of Ohio, where doctors at the University of Cincinnati Medical Center treated him. He had spent 17 months in captivity after being arrested in early 2016 for allegedly stealing a propaganda poster from his Pyongyang hotel.

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The North Koreans said that constituted a "hostile act" — and sentenced him to 15 years of hard labor. But after his parents said they heard nothing about their son for 15 months, the North Koreans last week allowed a State Department official to retrieve Warmbier and said he was being released on "humanitarian grounds."

American doctors said Warmbier suffered brain damage and was in a state of "unresponsive wakefulness." He was buried Thursday after a funeral attended by thousands.

Warmbier's parents said the North Koreans claimed their son had contracted botulism before taking a sleeping pill, which led him to slip into a coma. But doctors in Cincinnati said there were no signs of infection when he returned to America.

The unnamed ministry spokesman told state-run media on Friday that Warmbier was provided "with medical treatment and brought him back alive" after his heart had "nearly stopped."

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U.S. officials have not been able to provide a cause of death for Warmbier, in part because his family objected to an autopsy being performed.

President Donald Trump has also suggested that the Obama administration did not do enough to ensure Warmbier's freedom.

But a former Obama administration official told NBC News last week that there was "no higher priority than securing the release of Americans detained overseas" and that the U.S. "worked through every avenue available to us — including through the Swedish, our protecting power, and our representatives in New York — to secure the release of Mr. Warmbier."