WASHINGTON (REUTERS) - The director of the hospital in North Korea that treated an American student who died last year after detention in the country has rejected fresh charges that the death was a result of torture.

The official Korean Central News Agency quoted the director of the Pyongyang Friendship Hospital as saying on Saturday (Oct 27) that recent reports about the fate of 22-year-old Otto Warmbier, who died days after he was returned to the United States in a coma, were a "total distortion of the truth".

"The American doctors who came... to help Warmbier's repatriation acknowledged that his health indicators were all normal and submitted a letter of assurance to our hospital that they shared the diagnostic result of the doctors of our hospital," KCNA quoted the unnamed director as saying.

"Now the question is: What is the ulterior motive of those American doctors trying to make a different story at this point in time with regard to the cause of Warmbier's death?" the report said, adding that medical assessments "should not be influenced by any selfish purpose or political interest".

It added that Mr Warmbier's "health indicators were all normal" at the time of his release and there should instead be an investigation into the cause of his sudden death after his arrival in the US.

The KCNA report came hours after the Korean service of the Voice of America (VOA) radio station carried a report on a lawsuit filed by Mr Warmbier's parents alleging that their son was tortured in detention.

VOA quoted declarations filed in support of the suit by Mr Warmbier's former dentists as saying that there was evidence of trauma to his teeth.

It quoted another declaration from Dr Daniel Kanter, a neurologist who was the lead physician for Mr Warmbier on his return to his home town of Cincinnati, as saying that Mr Warmbier suffered brain damage after a cessation of blood flow to the brain for five to 20 minutes.

"Because the injury was so extensive, it was unlikely that Mr Warmbier was with medical personnel who were willing and able to intervene to resuscitate him when the injury occurred," Dr Kanter's declaration was quoted as saying.

North Korea has blamed botulism and ingestion of a sleeping pill for Mr Warmbier's condition. The coroner who examined Mr Warmbier said he found no sign of botulism, adding there was no evidence of trauma to Mr Warmbier's teeth or of broken bones.

US President Donald Trump charged last year that Mr Warmbier was tortured, but also held an unprecedented summit with the North Korean leader this year and is planning another aimed at persuading him to abandon a nuclear weapons programme that threatens the US.