"We haven't heard anything" about the reasons for the October 26 detention of Merrill Newman, who usually lives in a California retirement home, his son Jeff Newman told CNN television.
"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.
"This is a misunderstanding. My father is a (Korean War) veteran, and wanted to see the country and culture he has been interested in for years," Newman stressed.
"He had all the proper visas."
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Asked why the elderly man would travel to isolated North Korea, with which the United States has no relations, his son said it was a veteran's dream, calling his father a "curious cat."
"Just like World War II vets who have had an interest in going back to Normandy, my dad wanted to go back to the northern part of the peninsula," Jeff Newman said.
"He had been to the southern part of the peninsula before and this was a life-long dream of his."
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."
The reclusive North is also holding US national Kenneth Bae, a 45-year-old tour operator arrested a year ago as he entered the northeastern port city of Rason.
He was sentenced to 15 years' hard labour on charges of seeking to topple the government.
The court described Bae, also known by his Korean name Pae Jun-Ho, as a militant Christian evangelist who smuggled inflammatory material into the country and sought to establish a subversive base in Rason.