WASHINGTON/CINCINNATI (REUTERS) - Otto Warmbier, an American university student held prisoner in North Korea for 17 months and said by his family to be in a coma, was medically evacuated from the reclusive country after a rare visit there from a high-level United States official.

Warmbier, 22, a University of Virginia student from suburban Cincinnati, arrived in the United States on Tuesday (June 13) evening, witnesses said.

His release came after Joseph Yun, the US 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. "Sadly, he is in a coma and we have been told he has been in that condition since March of 2016," the parents said in a statement.

"We learned of this only one week ago. We want the world to know how we and our son have been brutalised and terrorised by the pariah regime in North Korea."

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 plane landed at Cincinnati Municipal Lunken Airport at around 10.15 pm local time (9.15am Singapore), according to a Reuters witness. Medical personnel carried a male, believed to be Warmbier and wearing a blue shirt and dark blue pants, off the plane without the use of a stretcher.

The person carried from the plane did not appear to be moving independently, the Reuters witness said.

A small group of family friends was nearby to celebrate Warmbier's arrival, cheering and holding signs that read "Pray for Otto" and "Welcome home Otto." The man was loaded into an ambulance bound for the University of Cincinnati Medical Center, where a hospital spokesman said he would receive treatment.

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.

Hours after his release, the US government blamed Pyongyang for a raft of cyber attacks stretching back to 2009 and warned more were likely.

BIG PRIORITY

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.

The State Department denied any connection between Warmbier's release and Rodman's visit, which President Donald Trump's administration said it did not authorise.

The State Department is continuing to discuss three other detained Americans with North Korea, US Secretary of State Rex Tillerson said.

Since taking office in January, Trump has faced a growing national security challenge from North Korea, which has conducted a series of ballistic missile tests in defiance of US and international sanctions.

White House spokeswoman Sarah Sanders told reporters on Air Force One that "bringing Otto home was a big priority for the president." In rare high-level contacts, Yun met senior North Korean officials in Oslo in May, where it was agreed Swedish officials in Pyongyang, who handle US consular affairs there, would be allowed to see all four American detainees, a State Department official said.

The North Koreans later urgently requested another meeting in New York. Yun met North Korea's ambassador to the United Nations on June 6 and was told about Warmbier's condition, the official said, speaking on condition of anonymity.

Tillerson consulted with Trump and arrangements were made for Yun and a medical team to travel to Pyongyang, the official said.

Yun arrived on Monday, visited Warmbier with two doctors and demanded his release, the official said. The North Koreans agreed and he was flown out on Tuesday. "In no uncertain terms North Korea must explain the causes of his coma," veteran former diplomat Bill Richardson said in a statement after speaking to Warmbier's parents. Richardson has played a role in past negotiations with North Korea.