(NEW YORK) — A U.S. service member who crossed into North Korea “without authorization” is in custody in the secretive country, United Nations and U.S. officials said Tuesday.

“A U.S. National on a JSA orientation tour crossed, without authorization, the Military Demarcation Line into the Democratic People’s Republic of Korea,” the United Nations Command said on Twitter. “We believe he is currently in DPRK custody and are working with our KPA counterparts to resolve this incident.”

The Joint Security Area, or JSA, sits in the Demilitarized Zone along the border between North and South Korea.

The soldier was identified as 23-year-old Pvt. Travis King, a U.S. official confirmed.

King had finished two months at a South Korean detention facility following an altercation with locals, according to the official.

Two other U.S. officials confirmed to ABC News King was released from the detention facility, then spent about a week at a U.S. base in South Korea under observation. He completed out-processing from the facility and on Monday was escorted to the Incheon International Airport as far as the customs checkpoint. The military escort had no ticket and was not allowed past the checkpoint, so King continued into the terminal alone.

He was supposed to board a flight and end up in Fort Bliss, Texas, according to the first official. But instead he ended up leaving the terminal for a DMZ tour. It is not clear when he bought a ticket.

Because King had finished serving his time, he was no longer under custody. An escort to the gate was not required, and there was no reason to suspect he would fail to board his flight.

The military will not publicly identity King until next of kin are notified. While “next of kin notification” is usually associated with the deaths of service members, in this case it’s not clear the soldier will ever return from North Korea, so the family notification process works similarly.

ABC News’ Joe Simonetti contributed to this report.

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