The North’s state-run Korean Central News Agency said that the American, identified as Bae Jun-ho, had entered the country on Nov. 3 through a port city near the Russian border. Human rights activists in South Korea said they believed Mr. Bae to be Kenneth Bae, 44, who they reported earlier this month was being held in the North.

In recent years, North Korea has detained several Americans, in some cases agreeing to free them only after high-profile Americans visited the North Korean capital, Pyongyang, to seek their release. Analysts have suspected North Korea’s leaders of trying to use such detentions to counter Washington’s diplomatic pressure over its nuclear and missile programs and force the United States to engage with them.