For unknown reasons, Private Travis King ran into North Korea while on a civilian tour of the Demilitarized Zone on Tuesday, a day after he was supposed to leave for a military base in the U.S. King, 23, had been released from a South Korean prison last week after serving nearly two months for assault.

The army has launched an investigation into the incident, Pentagon spokesperson Sabrina Singh said at a Thursday press conference. Army counterintelligence personnel will lead the inquiry, she added.

As of Thursday, Singh said the U.S. still had not had any communication from North Korea about the incident and emphasized that Washington wanted to bring King back to the U.S.

“We want to bring him home. We don’t know his condition. We don't know where he's being held. We don't know the status of his health,” she said. The Pentagon, National Security Council and State Department are “really pulling all levers of government here to try and find out more.

“This is a very difficult situation. I can't imagine what his family’s going through. All I can say is that our priority is to bring him home,” Singh said.

The U.S. State Department said Wednesday that Pentagon officials attempted without success to reach counterparts in the North Korean People’s Army. Swedish diplomatic officials have in the past provided consular services for Americans in dealing with North Korea, but reportedly have not returned to the country since Pyongyang ordered foreigners out of the country at the start of the COVID-19 pandemic.

The U.S. also can reach North Korea via a hotline at its border with South Korea at the U.S.-led U.N. Command in Panmunjom — known as the "pink phone."

But currently there are no known, active dialogues between North Korea and the U.S. or South Korea.

The U.S. and North Korea fought during the 1950-53 Korean War and are still technically at war since that conflict ended in a truce, not a peace treaty. They have no diplomatic ties.

One woman on the tour with King said she initially thought his sprint across the border was some kind of stunt until she heard an American soldier on patrol shouting for others to try to stop him.

King’s family members in the U.S. say he may have felt overwhelmed by his legal troubles while stationed in South Korea, offenses that could lead to his discharge from the U.S. military.

His immediate fate in North Korea was unknown, but the Pyongyang government has held Americans in the past and not quickly released them. Tensions between the two governments remain high.

On Wednesday, North Korea test-fired two ballistic missiles into the sea in an apparent protest of the deployment of a U.S. nuclear-armed submarine in South Korea for the first time in decades.

The arrival of the USS Kentucky, capable of launching Trident II ballistic missiles with a range of 12,000 kilometers, is a highly symbolic move signaling that Washington will stand with South Korea in the event of a North Korean nuclear attack.

Yang Moo-jin, president of the University of North Korean Studies in South Korea, told The Associated Press, "It's likely that North Korea will use the soldier for propaganda purposes in the short term and then as a bargaining chip in the mid- to long term.”

King was escorted as far as a customs checkpoint on Monday but left the airport before boarding his flight back to the U.S. It was not clear where he spent time before joining the Panmunjom tour at the border between North and South Korea Tuesday afternoon.

King’s time in South Korea was troubled. Aside from his recent jail term, a court last February fined him $3,950 for assaulting an unidentified person and damaging a police vehicle in Seoul last October.

In that ruling, a transcript of the verdict said King had also been accused of punching a 23-year-old man at a Seoul nightclub, though the court dismissed that charge because the victim didn't want King to be punished.

U.S. Defense Secretary Lloyd Austin said Tuesday that King “willfully and without authorization” crossed into North Korea. He said the U.S. was “closely monitoring and investigating the situation.”

“I’m absolutely foremost concerned about the welfare of our troops,” Austin said, “and so, we will remain focused on this.”

King is the first known American held in North Korea in nearly five years. Each detention has set off complicated diplomatic negotiations.

King's mother told ABC News she was shocked when she heard her son had run into North Korea.

"I can't see Travis doing anything like that," said Claudine Gates of Racine, Wisconsin.

Gates said she last heard from her son "a few days ago," when he told her he would return soon to Fort Bliss in the U.S. state of Texas. She added she just wanted "him to come home."

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 Korean War ended.(VOA/NJ)