North Korea on Thursday accused Donald Trump of exploiting the death of Otto Warmbier, referring to the US president as an "old lunatic" for alleging the American student was tortured while in Pyongyang's custody.

In a statement issued by the state-run KCNA news agency, North Korea's foreign ministry accused the US of "luring and pushing" 22-year-old Warmbier into breaking the country's laws.

"Trump and his clique, for their anti-DPRK propaganda, are again exploiting the death of Otto Warmbier," it said, using the acronym for the North's official name.
 

Warmbier, who was visiting North Korea as a tourist in January 2016 when he was arrested and imprisoned by the regime, died in June a few days after he was sent home in a mysterious coma after more than a year in prison in North Korea.

In the statement, the North accused "an anti-DPRK conspiracy organization in the U.S" of giving Warmbier a criminal "mission".

The US was now "employing even a dead person for the conspiracy campaign to fuel the international atmosphere of putting pressure on the DPRK", it said.

Warmbier's parents and Trump this week accused the reclusive regime of torturing the young man, who had been convicted of trying to steal a propaganda poster from a Pyongyang hotel.

"Otto was tortured beyond belief by North Korea," Trump said on Twitter.

The parents, in a series of TV interviews Tuesday, said their son showed signs of torture, including teeth that appeared to have been "rearranged," and hands and feet that were disfigured.

On Wednesday, an Ohio medical examiner said Warmbier displayed no obvious signs of torture. He had suffered brain damage caused by the lack of oxygen to the brain, the coroner said. (AFP)