US President Donald Trump has accused North Korea of abusing an American “student” who had been imprisoned in the Asian country for over a year over espionage charges.

Otto Warmbier, 22, spent 17 months in a North Korean jail over spying charges and was released to his family back in the US after falling into a coma due to a “severe neurological injury.” He died on June 19.

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

Pyongyang said Warmbier�s release had been based on a court decision and “on humanitarian grounds.” No further details were provided.

He had been convicted of crimes against the state for trying to steal a propaganda poster from a hotel in Pyongyang and sentenced to 15 years in prison.

The US president had previously accused Pyongyang�s "brutal regime" of Warmbier�s predicament but it was the first time he publicly blamed North Korea for torture in the case.

Trump’s tweet came after Fox News broadcast an interview with Warmbier�s parents.

"They kidnapped Otto, they tortured him, they intentionally injured him. They are not victims, they are terrorists," Warmbier�s father, Fred, said on Tuesday.

Following the young man’s death, the United States issued a ban prohibiting its citizens traveling to North Korea.

The measure was introduced after American officials said the risk of arrest by North Korean officials presented an "imminent danger to the physical safety" of US citizens. The ban came into effect on September 1.

North Korea has detained at least 17 American citizens over the past decade and three of them remain imprisoned there, according to official reports.