North Korea told the Swedish Embassy in Pyongyang about the detention and said it hasn't granted diplomats access to the person who was not named, State Department spokeswoman Jen Psaki told reporters.
The Swedish Embassy is negotiating on behalf of Merrill Newman because the U.S. has no diplomatic ties to North Korea.
In California, Newman's wife, Lee Newman, said in a prepared statement, "The family feels there has been some dreadful misunderstanding leading to his detention.
Her husband was set to end a 10 day tour of North Korea on Oct. 26. But just before he was slated to fly out, he was escorted from his flight by a North Korean official.
"We have had no word on the state of his health, whether or not the medications sent to him through the Swedish Embassy in North Korea have been delivered or why he was detained," she said.
Newman doesn't fit the pattern of other Americans detained by North Korea in recent years.
By all accounts, he wasn't a missionary or a journalist. He had no apparent political or religious agenda for the government of Kim Jong Un. Instead, he visited North Korea as a curious tourist, according to his son, eager to reconnect with a country where he'd served as an infantryman during the Korean War, six decades ago.
The mystery, then, about why Pyongyang has held him for a month has baffled Newman's friends and family — as well as analysts who study North Korea.
"We're concerned about him," said Barbara Ingram, a neighbor n the Channing House retirement community, an 11-story apartment house where the Newmans live.
"I find this pretty weird," Robert Kelly, a political scientist at Pusan National University in South Korea who has traveled as a tourist to North Korea, said of Newman's detention.
"I don't see any of the usual signs — such as missionary activity or overt law-breaking — that lead to detention."
Whatever the reasons behind the detention, it could hurt impoverished Pyongyang's efforts to encourage a growing tourism trade seen as a rare source of much-needed foreign currency. "This obviously jeopardizes North Korea's long, painstaking effort to build a tourism industry," Kelly said in an email.
Tourism is picking up in North Korea, despite strong warnings from the U.S. State Department, most recently this week, about the risk of arbitrary detention. Americans travel there each year, many as part of humanitarian efforts or to find long-lost relatives or to see a closed society few outsiders get to visit.
Newman has been described as an inveterate traveler and long-retired finance executive. His son, Jeffrey Newman, said his father wanted to return to the country where he spent three years during the Korean War.
North Korea has detained at least six Americans since 2009, including two journalists accused of trespassing and several Americans, some of whom are of Korean ancestry, accused of spreading Christianity.
Kenneth Bae, a Korean-American missionary and tour operator, has been detained for more than a year. North Korea sees missionary work as a Western threat to its authoritarian government.
It's possible that North Korea could try to use Newman as a diplomatic pawn in an interminable nuclear standoff with Washington — something analysts say Pyongyang has done previously with detained Americans. Several of them were only released after high-profile visits to Pyongyang by prominent Americans, including former Presidents Jimmy Carter and Bill Clinton.
While detaining a tourist is rare, said Yoo Ho-Yeol, a professor of North Korea studies at Korea University in Seoul, Newman's background as a war veteran, while probably not the main reason for his detention, may be a good way for Pyongyang to indirectly pressure Washington to resume long-stalled nuclear disarmament-for-aid talks and other issues.
"He's someone who the U.S. government would pay great attention to," Yoo said.
Pyongyang has called for a resumption of those nuclear talks, which have been stalled since 2008, but insists it must be recognized as a nuclear power. Washington balks at that and says talks won't happen until North Korea first shows signs it will abide by past nuclear disarmament commitments.
Another U.S. veteran of the Korean War, also named Merrill Newman was awarded the Silver Star in 1952 for leading his Marine platoon in a series of attacks that inflicted heavy casualties on North Korean troops and for taking effective defensive actions during a massive counter-attack, according to the Military Times.
But Jeffrey Newman has told reporters that there's no indication North Korean authorities have confused his father with the other Merrill Newman, who is now 84 and lives in Oregon.
"I have no idea why this guy was detained and whether they had Googled — liked anybody else can — the name and found me and thought this guy was me or whatever," said the Beaverton, Oregon-based Merrill Newman.
Korean War veteran Thomas Hudner, a retired Navy captain and Medal of Honor winner, went to North Korea in July to fulfill a promise he said he made 60 years ago to recover the remains of a pilot who was trapped in his downed fighter jet. While in North Korea, Hudner "didn't mention the war at all" and said he had no complaints about how he was treated.
Still, the Korean War service of American tourists in North Korea could be sensitive. That conflict ended in an armistice, not a peace treaty, leaving the Korean Peninsula still technically at war — something Pyongyang's propaganda frequently raises in criticism that Washington and Seoul seek to bring down its government.
Kim Dong-jil, a South Korean professor who is deputy director of Peking University's Center for Korean Peninsular Studies, said a low profile by the U.S. government and media could lead to Newman's quick release.
"The North Korean authorities know it would do no good to detain an elderly man for a long time because of human rights concerns," he said.