ASPEN, Colo. — The American soldier who crossed into North Korea “may not have been thinking clearly,” the Army’s top civilian said Thursday, adding that she’s worried about his safety.

Pvt. Travis King, who was headed back to the United States after spending time in a South Korean prison for assault, opted instead to cross the heavily armed border into repressive North Korea on Tuesday while he was part of a tour group. Washington has failed to make contact with Pyongyang since the incident.

Army Secretary Christine Wormuth refused to ascribe a motivation but hinted that King was likely stressed about his situation.

“He is a young soldier, he was facing consequences. I imagine he had a lot of negative feelings,” she told an audience at the Aspen Security Forum. “He may not have been thinking clearly, frankly, but we just don’t know.”

Wormuth added that she’s concerned for King’s safety due to North Korea’s history of mistreating American citizens — in some cases leading to death.

“What we want to do is get that soldier back into our custody. I worry about him, frankly,” she said, noting how the North Koreans released college student Otto Warmbier in 2017 while he was in critical condition. He died in a hospital six days after his return to the United States. “It makes me very, very concerned that Pvt. King is in the hands of the North Korean authorities. I worry about how they may treat him.”

The Biden administration has tried to engage with North Korea via multiple channels, including through United Nations Command, which is led by U.S. Army Gen. Paul LaCamera.

“I can tell you this morning we’ve now reached out through multiple channels to the KPA to try to ascertain that information and to get closer to an answer,” White House deputy press secretary Olivia Dalton told reporters Thursday.

Lara Seligman and Kaitlyn Locke contributed to this report.