The launches followed a separate round of North Korean cruise missile tests last week and a Jan. 14 test-firing of the country’s first solid-fuel intermediate-range ballistic missile. Those tests reflect North Korean leader Kim Jong Un’s efforts to expand his arsenal of weapons designed to overwhelm missile defenses in South Korea and Japan and remote U.S. targets in the Pacific, including Guam.

South Korea’s Joint Chiefs of Staff said they detected the missiles over waters near the North Korean port of Sinpo, where the North has a major shipyard building key naval vessels, including missile-firing submarines.

The South’s military didn’t immediately provide specific launch details, including the number of missiles fired, how far they flew and whether they were launched from land or naval assets.

Tensions on the Korean Peninsula have increased in recent months as Kim continues to accelerate his weapons development and issue provocative threats of nuclear conflict with the U.S. and its Asian allies.

The U.S., South Korea and Japan in response have been expanding their combined military exercises, which Kim portrays as invasion rehearsals, and sharpening their deterrence strategies built around nuclear-capable U.S. assets.

North Korea said its launches last week involved a new cruise missile called Pulhwasal-3-31 and described the test as part of regular efforts to develop its military. The North described that missile as “strategic,” implying a possible intent to arm it with nuclear weapons.