Image caption Merrill Newman has reportedly been interested in North Korean culture for years

US officials are urging North Korea to "let our citizens go free", as reports say that an 85-year-old US veteran has been detained in the country.

Merrill Newman, a Korean War veteran, was taken off a plane by uniformed officers at the end of a guided tour in North Korea last month, his son said.

US officials have not specifically confirmed the case, but have called on North Korea to "resolve the issue".

Another US citizen, Kenneth Bae, has been detained since last November.

Mr Newman visited North Korea with a friend in October, his son, Jeffrey Newman said on Thursday.

The guided tour was arranged with a travel agent "approved by the North Korean government for travel of foreigners", he added.

Merrill Newman was taken off a plane on 26 October, the last day of his tour, as he was set to leave North Korea, Jeffrey Newman said.

The veteran appeared to have discussed his experience in the Korean War with North Korean officials the day before his detention, his son added.

Another veteran, also named Merrill Newman, was awarded a Silver Star medal for his efforts during the Korean War. In an interview with Reuters news agency, he said that he thought it was possible there had been "a case of mistaken identity".

'Arbitrary arrest'

When asked about Mr Newman's detention, US Secretary of State John Kerry would not comment directly on the case, but said: "They have other people, too... These are all very, very disturbing choices by the North Koreans."

US Special Representative for North Korea Policy Glyn Davies, said: "We are calling on North Korea, as in the Kenneth Bae case, to resolve this issue and let our citizens go free."

He added that he could not comment specifically about Mr Newman's case "because we do not have a privacy act waiver".

The US State Department revised its travel guidance for North Korea this week, saying: "US citizens crossing into North Korea, even accidentally, have been subject to arbitrary arrest and long-term detention."

However, a small number of tourists do enter North Korea every year.

Travel to North Korea is tightly controlled, with tourists only able to visit through tour companies that are accompanied by local guides.

US troops backed South Korea in the 1950-1953 Korean War, which killed at least two million people.