TOKYO — North Korea appears to have launched another missile into the sea between the Korean Peninsula and Japan on Saturday morning, in what would be its first launch this month.

The launch would coincide with joint exercises between the U.S. and South Korean militaries, exercises that North Korea always strongly protests because it considers them preparation for an invasion.

South Korea’s Joint Chiefs of Staff said that a “projectile” had been fired on Saturday morning and that it was working to determine what kind of missile it was, according to the South’s Yonhap News Agency.

South Korea’s president, Moon Jae-in, had been informed, Yonhap said.

Japanese authorities determined it was a ballistic missile launched from a site in Gangwon province on North Korea’s east coast, Japan’s NHK broadcaster and Kyodo News reported.

U.S. Pacific Command in Hawaii, which monitors North Korean missiles, did not immediately comment on the launch.

The Ulchi Freedom Guardian exercises, which mainly involve computer simulations rather than battlefield maneuvers or fly-overs with bombers, are currently taking place in South Korea.

Last month North Korea fired its first intercontinental ballistic missiles, technically capable of reaching the mainland United States, and this month warned that it was considering launching missiles into the Pacific Ocean near the American territory of Guam.