The United States dispatched a ballistic submarine to South Korea on Tuesday for the first time in decades amid escalating tensions on the peninsula with North Korea.

“As we speak, an American nuclear submarine is making port in Busan today,” the White House’s Indo-Pacific coordinator, Kurt Campbell, told reporters during a press conference on Tuesday in Seoul.

The ship, the USS Kentucky, is an Ohio-class submarine and “reflects the United States’ ironclad commitment to the Republic of Korea for our extended deterrence guarantee,” the Pentagon said in a statement. The vessel, anchored in the south of the country, marked the first time a submarine with nuclear capabilities had made a port call to South Korea since the 1980s, the country’s defense ministry reported.

In response, North Korean forces launched two short-range ballistic missiles (SRBM) off its eastern coast on Wednesday morning (local time).

In an unrelated incident, an American soldier was detained after crossing the international border and entering North Korea without permission on Tuesday.

“A U.S. Service member on a JSA [Joint Security Area] orientation tour willfully and without authorization crossed the Military Demarcation Line into the Democratic People’s Republic of Korea (DPRK). We believe he is currently in DPRK custody and are working with our KPA counterparts to resolve this incident,” Colonel Isaac Taylor, a public affairs aide with the United States Forces Korea (USFK), said in a statement.

Secretary of Defense Lloyd Austin reiterated the statement when asked about the detained soldier during a press conference on Tuesday. “I’m absolutely foremost concern about the welfare of our troop, and so we will remain focused on this and, again, this will develop in the next several days and hours, and we’ll keep you posted,” the secretary said.

Unnamed American officials identified the soldier as Private 2nd Class Travis King, the Associated Press first reported. King was released from a South Korean jail where he was being held on assault charges and facing additional military disciplinary actions in the United States.