North Korea on Thursday called President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE an "old lunatic."

The country was firing back against allegations by Trump, among others, that an American college student who died after being held in the country for 17 months was tortured and disfigured while in custody.

In a statement carried by state-run media, a spokesman for North Korea's foreign ministry accused Trump and others of using "bogus data" to claim that Otto Warmbier, who died in June shortly after returning to the U.S., was badly mistreated in North Korea.

"The fact that the old lunatic Trump and his riff-raff slandered the sacred dignity of our supreme leadership using bogus data full of falsehood and fabrications, only serves to redouble the surging hatred of our army and people towards the U.S. and their will to retaliate thousand-fold," the state-broadcaster KCNA quoted the spokesman as saying, according to AFP.

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An Ohio coroner said Wednesday that Warmbier, 22, had died of a lack of blood and oxygen to his brain due to an unknown injury he sustained more than a year earlier.

Warmbier's parents refused an autopsy of their son's body, and only a physical examination and CT scan were conducted. The coroner said that what ultimately caused Warmbier's death remains a mystery, though his body appeared to be in good condition.

After Warmbier's parents said in a Fox News interview that the North Koreans had "destroyed" their son, Trump tweeted on Tuesday that the University of Virginia student "was tortured beyond belief by North Korea."

Warmbier was arrested while touring North Korea through a Chinese company. North Korean officials alleged that he had attempted to steal a propaganda poster and he was sentenced to 15 years of hard labor.

But the student was returned to the U.S. in a comatose state in June. North Korean officials said he had contracted botulism and taken a sleeping pill.

North Korea's rebuttal of the torture allegations comes amid a deepening war of words between Trump and Pyongyang. Tensions between the two countries rose to new heights this week, when North Korea's foreign minister said that Trump's threats against the country amounted to a declaration of war.

While the White House rejected that notion as "absurd," international concerns have grown that the U.S. and North Korea may be hurdling toward a confrontation.