LOS ANGELES (AFP) - North Korea has detained for more than three weeks an 85-year-old American retiree who was on an organized tour due to an "misunderstanding," friends and relatives said Wednesday.

The US special envoy on North Korea, Mr Glyn Davies, without naming detainee Mr Merrill Newman by name, called on North Korea to release Americans it is holding.

Korean war veteran Newman's son Jeff said "we haven't heard anything" about the reasons for the October 26 detention. "We worked through the State Department from the day that he was supposed to depart... That started the diplomatic wheels turning, but we've heard nothing," the younger Newman told CNN television.

"This is a misunderstanding. My father is a veteran, and wanted to see the country and culture he has been interested in for years." The day before he was to depart, Newman met with North Korean officials, who discussed his Army service in the war more than 50 years earlier, the son told the San Jose Mercury News in California.

The next day, five minutes before take-off on the plane taking him out of the country, he was escorted off the plane, Jeff Newman said. The elder Newman, who usually lives in a California retirement home, "arranged this with a travel agent that was recommended and said was approved by the North Korean government for travel of foreigners," his son insisted on CNN.

"He had all the proper visas." Media reports suggested that Newman had traveled to North Korea with a friend from Channing House, a retirement home in Palo Alto, outside San Francisco. His traveling companion, named as Bob Hamrdla, also called his friend's detention "a terrible misunderstanding." "I hope that the North Koreans see this as a humanitarian matter and allow him to return to his family as soon as possible," said Mr Hamrdla, in a statement cited by the San Jose Mercury News.

On Tuesday, the agency issued an updated travel advisory, urging Americans to avoid North Korea, which reportedly was "arbitrarily detaining US citizens and not allowing them to depart the country."

Washington's special envoy Davies, who was visiting Beijing, told journalists Wednesday that he had seen reports of the detention but could not comment because of the US Privacy Act. The US was "working very hard" through the Swedish embassy in Pyonyang "to try to move this issue along," he said.

North Korea has in the past freed detained Americans after visits from high-level emissaries.