U.S. Defense Secretary Lloyd Austin said on Tuesday that a U.S. servicemember who  crossed the heavily armed inter-Korean border into North Korea did so of his own volition.

Austin made the remarks during a press conference at the Pentagon when asked about the incident, saying that the soldier, who was reportedly on a civilian tour of the Demilitarized Zone, "willfully and without authorization" separated from the group and crossed the demarcation line.

The secretary said that the soldier is believed to be in North Korean custody and the U.S. is closely monitoring and investigating the situation and working to notify his next of kin.

Asked if he was concerned about any possible impact the incident may have on security, Austin said that the welfare of the servicemember is his foremost concern and will remain the focus of the U.S.

White House spokesperson Karine Jean-Pierre also confirmed on Tuesday that a U.S. soldier voluntarily crossed the military demarcation line into North Korea unauthorized, adding that the Pentagon has reached out to their counterparts in the North.