WASHINGTON -- A coroner said Wednesday her office could not determine the exact cause of the death of Otto Warmbier, an American college student who was detained in North Korea for more than a year.

Lakshmi Sammarco, a coroner in Cincinnati, Ohio, told reporters the University of Virginia student had brain damage caused by oxygen deprivation, but it's unclear what led to that, according to multiple news reports.

Warmbier died in June, several days after he was returned home to Ohio in a coma. The 22-year-old was arrested in North Korea in January 2016 for allegedly stealing a propaganda poster from a hotel and sentenced to 15 years of hard labor.
 

In a report signed Sept. 11, Sammarco's office said the oxygen deprivation resulted from "an unknown insult more than a year prior to death," the AP said.

NBC News quoted the coroner as saying there was no evidence of torture, an accusation made by Warmbier's parents and promoted by President Donald Trump.

"We believe that for somebody who had been bedridden for more than a year, that his body was in excellent condition, that his skin was in excellent condition," she was quoted as saying.

The coroner's office performed a physical examination of the body, not a full autopsy, at the request of Warmbier's parents.

North Korea has denied charges of torture, saying he fell into a coma two months after his arrest due to botulism and a sleeping pill. Doctors in the US found that he suffered from severe brain damage.

The US has since imposed a ban on Americans traveling to the communist nation, citing serious risks to their safety. (Yonhap)