CHICAGO • Otto Warmbier, the American student who died days after being released from North Korea in a coma, displayed no obvious signs of torture despite assertions by his parents and US President Donald Trump, an Ohio medical examiner said.

Coroner Lakshmi Sammarco on Wednesday said the 22-year-old, who had been sentenced to 15 years' hard labour while visiting the North, had suffered brain damage caused by lack of oxygen, but could not say what caused the injury.

The revelations came a day after Mr Warmbier's parents and Mr Trump accused Pyongyang of torturing the young man, who had been convicted of trying to steal a propaganda poster from a hotel.

The parents, in a series of TV interviews on Tuesday, said their son showed signs of torture, including teeth that appeared to have been "rearranged". After the broadcast, Mr Trump for the first time accused the North Korean regime of torturing the student.

But Ms Sammarco said Mr Warmbier's body showed only a few small scars, all but one of which could be traced to medical instruments.

Meanwhile, North Korea yesterday accused Mr Trump of exploiting Mr Warmbier's death, calling the US President an "old lunatic".

"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 US and their will to retaliate thousand-fold," said a statement by the official KCNA news agency.

AGENCE FRANCE-PRESSE