North Korea launched two short-range missiles into its eastern sea early Wednesday morning just a day after the U.S. docked its nuclear submarine in South Korea.

The move comes as tensions remain high between the two countries due to more frequent missile test launches by North Korea and the arrival of the nuclear-armed submarine.

South Korea’s Joint Chiefs of Staff said North Korea fired the ballistic missiles from near its capital of Pyongyang between 3:30 a.m. and 3:46 a.m. Wednesday. The missiles flew about 341 miles before landing in the eastern waters of the Korean peninsula.

Japanese Defense Minister Yasukazu Hamada also said they reached a maximum altitude of 31 miles and noted the missiles may have experienced an “irregular maneuver.”

The USS Kentucky arrived Tuesday afternoon at the port of Busan, which is the first visit by a U.S. nuclear submarine to South Korea since the 1980s.

“This port visit reflects US’ ironclad commitment to the ROK [South Korea] for our extended deterrence guarantee, and complements the training, operations and other military cooperation activities conducted by Strategic Forces to ensure they are available and ready to operate around the globe,” U.S. Forces Korea said in a statement.

This new launch is about a week after North Korea launched its first intercontinental ballistic missile (ICBM) in three months.

This also comes as the American-led United Nations Command and U.S. officials attempt to negotiate the release of an American soldier who “willfully” crossed the North Korean border from South Korea. The soldier has been identified as Pvt. 2nd Class Travis King, who was just released from a South Korean prison where he was doing time for assault charges.

Instead of going back to the U.S. on a plane, he chose to leave and join a tour of Panmunjom, a border village in the Demilitarized Zone, where he ran across the North Korean border, according to U.S. officials.

The Associated Press contributed.