ABC News has learned that the U.S. soldier was identified as Travis King.
LONDON -- An American soldier who had just been released from a South Korean detention facility fled across the border to North Korea where he was taken into custody this month.
Here's what we know about the situation.
The soldier in question was identified as 23-year-old U.S. Army Private 2nd Class Travis King, according to a U.S. official. King has been a cavalry scout in the U.S. Army since January 2021 and has no deployments, according to service information provided by Army spokesperson Bryce Dubee.
King has received three medals while serving in the U.S. military: the National Defense Service Medal, the Korean Defense Service Medal and the Overseas Service Ribbon. These medals are commonly received by American service members in Korea.
King served 47 days in a South Korean detention facility following an altercation with locals, according to a U.S. official.
South Korean media reported that King allegedly punched someone in the face repeatedly while drinking at a club in Seoul last September. He also allegedly kicked and broke the door of a police patrol car that was sent to the scene of a reported assault in Seoul last October, according to South Korean media.
After finishing his sentence, King was released from the detention facility on July 10, according to The Associated Press.
Two U.S. officials told ABC News that King spent about a week under observation at a U.S. military base in South Korea after being released from jail. He completed out-processing from the facility and on July 17 was escorted by U.S. military officials to South Korea's 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, according to the U.S. officials.
A U.S. official told ABC News that King was supposed to board a flight and end up in Fort Bliss, Texas. Awaiting him there was a "pending administrative separation actions for foreign conviction," another U.S. official said.
Because King had finished serving his sentence, he was no longer under custody and, thus, an escort to the gate was not required. There was also no reason to suspect he would fail to board his flight.
But instead, King left the airport terminal for a tour of the Korean Demilitarized Zone, or DMZ, the heavily militarized border that separates North and South Korea. It's unclear when he bought a ticket for the tour.
While on the tour, the soldier "wilfully and without authorization crossed the military demarcation line," according to U.S. Secretary of Defense Lloyd Austin, who didn't identify King by name.
"We're very early in this event and so there's a lot that we're still trying to learn," Austin told reporters on Tuesday. "We believe that he is in DPRK custody. We're closely monitoring and investigating the situation, and working to notify the soldier's next of kin and engaging to address this incident."
"I'm absolutely foremost concerned about the welfare of our troop. We will remain focused on this, and this will develop in the next several days," he added.
The United Nations Command also confirmed the incident via Twitter on Tuesday, saying an American "on a JSA orientation tour crossed, without authorization, the Military Demarcation Line into the Democratic People's Republic of Korea." The Joint Security Area, or JSA, sits in the DMZ along the border between North and South Korea.
"We believe he is currently in DPRK custody and are working with our KPA counterparts to resolve this incident," the U.N. command tweeted.
King's mother, Claudine Gates, who lives in Racine, Wisconsin, said she was shocked when she heard her son had crossed into North Korea.
"I can't see Travis doing anything like that," Gates told ABC News during an interview on Tuesday.
Gates said the U.S. Army told her on Tuesday morning that King had crossed into North Korea. She said she last heard from her son "a few days ago," when he told her would return soon to his base in Fort Bliss.
She told ABC News that she just wants "him to come home."
U.S. President Joe Biden has been briefed on the situation, while the U.S. Department of Defense and the U.S. Department of State work with the U.N. "to ascertain more information and resolve this situation," according to White House press secretary Karine Jean-Pierre, who declined to say how much political capital the Biden administration would expend to secure the soldier's safe return.
"I don't have more to share beyond that," Jean-Pierre told reporters on Tuesday. "We are looking into this."
ABC News' Joohee Cho, Luis Martinez, Martha Raddatz, Matt Seyler and Joe Simonetti contributed to this report.