SEOUL (Reuters) - North Korea said on Thursday (June 15) it has released American Otto Warmbier "on humanitarian grounds" after he had been held prisoner for 17 months.

Warmbier, 22, a University of Virginia student from suburban Cincinnati, was medically evacuated to the United States on Wednesday. His family said he arrived in a state of coma.

The North's KCNA news agency said in a one-sentence dispatch that Warmbier's release followed a court decision on Tuesday. It did not provide other details.

"Under a decision by the DPRK Central Court of June 13, American citizen Otto Warmbier who was serving a sentence of labour was returned on June 13 on humanitarian grounds," KCNA said.

DPRK is short for the North's formal name, the Democratic People's Republic of Korea.

Warmbier's release came after Joseph Yun, the U.S. State Department's special envoy on North Korea, travelled to Pyongyang and demanded Warmbier's release on "humanitarian grounds,"capping a flurry of secret diplomatic contacts, a US official said.

Warmbier's parents, Fred and Cindy, confirmed their son was on a medevac flight.

Warmbier was detained in January 2016 and sentenced to 15 years of hard labour in March last year for trying to steal an item with a propaganda slogan, according to North Korean media.

Warmbier's family said they were told by North Korean officials, through contacts with American envoys, that Warmbier fell ill from botulism some time after his March 2016 trial and lapsed into a coma after taking a sleeping pill, the Washington Post reported.

The New York Times quoted a senior US official as saying Washington recently received intelligence reports that Warmbier had been repeatedly beaten in custody.

Warmbier's release came as former US basketball star Dennis Rodman arrived in North Korea on Tuesday, returning to the nuclear-armed country where he met leader Kim Jong Un on previous visits.