Updated

A plainclothes American soldier has been detained in North Korea Tuesday after crossing the Military Demarcation Line separating the country from South Korea, U.S. officials tell Fox News.

A senior defense official tells Fox News that Private 2nd Class Travis King had just finished about two months in a South Korean detention facility following a physical altercation with locals. After King was arrested and throughout the time he was held at the facility he made comments that he did not want to come back to America, according to the official.  

A U.S. Forces Korea spokesperson said King was on a joint security area orientation tour on Tuesday when he "willfully and without authorization crossed the Military Demarcation Line into the Democratic People’s Republic of Korea (DPRK)."

"We believe he is currently in DPRK custody and are working with our KPA (Korean People's Army) counterparts to resolve this incident," the spokesperson added.

NORTH KOREAN AMBASSADOR MAKES RARE APPEARANCE AT UN, BLAMES US FOR ESCALATION

North Korea South Korea border crossing

In this photo taken on May 9, 2023, South Korean soldiers walk at the truce village of Panmunjom in the Joint Security Area (JSA) of the Demilitarized Zone (DMZ) separating North and South Korea, with a view of North Korea's Panmon Hall in the background. (Anthony Wallace/AFP via Getty Images)

King, who is serving under U.S. Forces Korea and the U.S. Army, was due to face disciplinary action from military officials, a senior U.S. defense official has told Fox News.

Prior to his detainment by Kim Jong Un's regime, King was released from the South Korea detention facility and spent about one week under observation at a U.S. base in South Korea. 

King was supposed to board a flight to go back to the U.S. and was escorted to an airport. But the military escort could not follow him past airport security, so King entered the terminal by himself with no escort. 

King later was alone Tuesday when he left the airport terminal for the tour of the DMZ. 

King was to be separated from the military for cause, and was supposed to go back to the U.S., according to an official that spoke to Fox News, but he missed his flight.

Map of where North Korea detained US soldier

The location of where a U.S. soldier reportedly crossed the Military Demarcation Line and was detained by North Korea, on Tuesday, July 18, 2023. (Fox News)

A U.S. defense official also told Fox News the soldier was on a tour in a personal capacity and was wearing civilian clothes at the time of the incident.

NORTH KOREAN AMBASSADOR MAKES RARE APPEARANCE AT UN, BLAMES US FOR ESCALATION

North Korea's state media has not commented on the matter.

"There are a lot of unanswered questions and I can tell you our U.S. military right now is mounting a full investigation," Dan Hoffman, a former CIA station chief, told "Fox & Friends". "I'm sure they are talking to anyone at that demilitarized zone who might have witnessed the soldier crossing over into North Korean territory. That is one of the most heavily surveilled geographic areas on the planet."

"Now North Korea has another piece of leverage that they can use against us and we know from the past that they have used U.S. persons as pawns to gain traction and negotiations with the United States," Hoffman added.

South Korean soldiers at border

South Korean soldiers stand guard during a media tour of the Joint Security Area (JSA) in the Demilitarized Zone (DMZ) in the border village of Panmunjom in Paju on March 3, 2023.  (Jeon-Heon-Kyun/AFP via Getty Images)

A State Department spokesperson told Fox News Digital it is "aware of reports from the Department of Defense that a U.S. service member willfully and without authorization crossed the Military Demarcation Line into the Democratic People’s Republic of Korea," but "Due to privacy considerations, we have no further comment at this time."

U.S. Defense Secretary Lloyd Austin also said "We're closely monitoring and investigating the situation and working to notify the soldier's next of kin and engaging to address this incident. 

"In terms of my concerns, I'm absolutely foremost concerned about the welfare of our troop," Austin added. "And so we will remain focused on this."

The State Department advises Americans not to travel to North Korea "due to the continuing serious risk of arrest and long-term detention of U.S. nationals."

"The U.S. government is unable to provide emergency services to U.S. citizens in North Korea as it does not have diplomatic or consular relations with North Korea," it adds in a travel advisory.

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Cases of Americans or South Koreans defecting to North Korea are rare, though more than 30,000 North Koreans have fled to South Korea to avoid political oppression and economic difficulties since the end of the 1950-53 Korean War, according to The Associated Press.

The Korean border village of Panmunjom, located inside the 154-mile-long Demilitarized Zone, was created at the close of the Korean War. The area is jointly overseen by the U.N. Command and North Korea.

The Associated Press contributed to this report.