It wasn't clear what led to the detention. The son said he was speaking regularly with the U.S. State Department about his father, but U.S. officials wouldn't confirm the detention to reporters, citing privacy issues.
North Korea's official state-run media have yet to comment on reports of the detention, which first appeared in the San Jose Mercury News and Japan's Kyodo News service.
Secretary of State John Kerry told MSNBC on Thursday in response to a question about Newman that North Korea needed to recognize the "dangerous steps that it's been taking on many fronts," including the treatment of its citizens and the start-up of its nuclear reactor.
"We are anxious to proceed to negotiations about denuclearization and to move away from these kinds of provocative actions," he said.
Kerry stopped short of confirming Newman's detention and said the country had "other people."
Newman's son said that, according to his father's traveling companion, Newman earlier had a "difficult" discussion with North Korean officials about his experiences during the 1950-53 war between U.S.-led United Nations forces and North Korea and ally China. That war ended in an armistice, not a peace treaty, leaving the Korean Peninsula still technically at war.
The war is still an important part of North Korean propaganda, which regularly accuses Washington and Seoul of trying to bring down its political system statements analysts believe are aimed in part at shoring up domestic support for young leader Kim Jong Un.
Another U.S veteran of the Korean War 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.
Jeffrey Newman told the San Jose Mercury News there is no indication North Korean authorities have confused his father with the other Merrill Newman, who is now 84 and lives in Oregon.
Contacted by the Mercury News, the veteran, Merrill Newman, said "it is kind of creepy" knowing someone with the same name was being held captive.
"It's a darn shame for that guy. I hope they get him out soon," he told the newspaper, adding he hasn't traveled to North Korea since the war. "I've been there, done that, and I don't want to go back."
The detention comes about a year after North Korea detained another American and as the U.S. State Department warns in a formal notice that Americans should avoid travel to the country, in part because of the risk of arbitrary arrest and detention.
North Korea has detained at least six Americans since 2009, often for alleged missionary work, but it is unusual for a tourist to be arrested. The North's secretive, authoritarian government is sensitive about foreign travelers, and tourists are closely monitored. Analysts say it has used detained Americans as diplomatic pawns in a long-running standoff with the United States over the North's nuclear bomb production, something it denies.
Speaking Thursday to reporters in Beijing, U.S. Special Representative for North Korea Policy Glyn Davies wouldn't confirm Newman's detention but said, generally, that Washington was working with the Swedish Embassy in Pyongyang, which acts as America's protecting power because Washington and Pyongyang don't have official diplomatic relations, "to try to move this issue along and of course calling on North Korea ... to resolve the issue and to allow our citizens to go free."
Washington also has expressed worry about the health of American Kenneth Bae, a missionary and tour operator who was sentenced to 15 years of hard labor after being arrested in North Korea last November for alleged hostile acts.
Merrill Newman was traveling with his friend, Bob Hamrdla, who was allowed to return. Hamrdla said in a statement that "there has to be a terrible misunderstanding" and asked for Newman to be quickly returned to his family.
Jeffrey Newman said his father always wanted to visit North Korea and took lessons in the language before leaving on the nine-day trip. Newman said he believed the inspiration came from the three years his father spent as an infantry officer in the Korean War, but said his father never talked about his service.
Jeffrey Newman said the Swedish ambassador had delivered his father's heart medication to the North Korean Foreign Affairs Ministry, but it was unclear whether he had received it.
Jeffrey Newman said he believed North Korea would eventually release his father after realizing that all they have is an "elderly traveler, a grandfather with a heart condition."
"We don't know what this misunderstanding is all about," he said. "All we want as a family is to have my father, my kids' grandfather, returned to California so he can be with his family for Thanksgiving."
Americans celebrate the Thanksgiving holiday next week.
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