Korean War veteran Merrill E. Newman, accompanied by his wife, Lee, speaks to the press after arriving at San Francisco International Airport on Saturday following his release from detention in North Korea. Photo: AFP

An 85-year-old Korean War veteran held for more than a month by North Korea as a war criminal arrived in San Francisco on Saturday to be reunited with his family.

North Korea detained Merrill E. Newman for crimes it accused him of committing during the conflict six decades ago as a member of the US special forces. He was released for humanitarian reasons after he apologized, the country's state news agency said.

Newman flew to China, where he boarded an 11-and-a-half-hour flight home. His United Airlines flight landed about 9 am.

Accompanied by half a dozen police officers, Newman looked in good health and held his wife's hand before walking up to a podium to briefly address the press at the airport's arrivals hall.

"I'm delighted. It's been a great homecoming," a smiling Newman told reporters. "I'm tired, but I'm ready to be with my family."

He was visiting North Korea as a tourist when he was pulled off an Air Koryo flight in Pyongyang minutes before it was due to depart for Beijing on October 26.

A senior Obama administration official said the Swedish Embassy in Pyongyang had been "heroic" in its efforts to get to see Newman but he suggested it was ultimately a mystery why the North Koreans chose to release him.

"Who knows? We can only speculate," said the official, who spoke on condition of anonymity.

The official added that "all efforts are now on (Kenneth) Bae," referring to another US citizen detained by North Korea since November 2012.

Bae, a Korean American who worked as a Christian missionary, was convicted by North Korea in May of crimes against the state. He has been serving a 15-year hard-labor sentence.

US Vice President Joe Biden, who is visiting South Korea, spoke with Newman after his release.

"It's a positive thing they have done, but they have Mr Bae, who has no reason for being held in the North and should be released immediately and we are going to continue to demand his release as well," Biden said.

Separately, a State Department spokeswoman declined comment on Newman's well-being and treatment in North Korea, referring such questions to his family.

Asked by reporters in San Francisco how the food was during his detention, Newman replied, "healthy," but he declined to answer other questions about his stay.

Asked if he would return to North Korea, he said, "Probably not."

Newman served during the 1950-53 Korean War and worked with Korean anti-Communist guerrillas fighting behind the lines against the socialist North.

The Democratic People's Republic of Korea, as the country is officially called, has called him a war criminal.

Reuters