Defense Secretary Lloyd Austin on Tuesday confirmed that a U.S. soldier being detained by North Korea “willfully and without authorization” crossed the border from South Korea into the pariah state.

“We’re very early in this event, and so there’s a lot that that we’re still trying to learn but what we do know is that one of our service members who was on a tour willfully and without authorization crossed the military demarcation line,” Austin told reporters at the Pentagon.

The soldier is believed to be in North Korean custody and U.S. officials are “closely monitoring and investigating the situation, and working to notify the soldier’s next of kin and engaging to address this incident,” Austin added.

“I’m absolutely foremost concerned about the welfare of our troops. And so we will remain focused on this,” he added.

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