North Korea fired a ballistic missile toward its eastern waters Monday morning, the South Korean military said, days after the end of the South Korean-U.S. military drills that the North views as an invasion rehearsal.South Korea's Joint Chiefs of Staff gave no further details, such as how far the weapon flew.Japan's Defense Ministry said it also detected a missile launch by North Korea, and the Japanese coast guard said a suspected North Korean missile landed in the ocean.Related video above: North Korea recently issued a clear warning to the U.S. and South Korea in response to annual joint military exercises.About 30 minutes after the North's launch, the Japanese coast guard issued a fresh emergency notice over a possible second missile launch by North Korea. South Korea's military couldn't immediately confirm the additional North Korean launch.It's the North's first known missile test since it carried out cruise missile launches in mid-February.During the South Korea-U.S. military drills that ended Thursday, North Korean leader Kim Jong Un guided a series of military training exercises involving tanks, artillery guns and paratroopers. But the North didn't perform any missile tests during its rivals' training.The 11-day South Korean-U.S. drills involved a computer-simulated command post training and 48 kinds of field exercises, twice the number conducted last year.Animosities on the Korean Peninsula remain high in the wake of North Korea's barrage of missile tests since 2022. Many of the tests involved nuclear-capable missiles designed to attack South Korea and the mainland U.S. The U.S. and South Korean forces have responded by expanding their training exercises.This year, North Korea performed six rounds of missile tests before Monday's launch.Experts say North Korea likely believes a bigger weapons arsenal would increase its leverage in future diplomacy with the United States. They say North Korea would want to win extensive sanctions relief while maintaining its nuclear weapons.Worries about North Korean military moves have deepened since Kim vowed in a speech in January to rewrite the constitution to eliminate the country's long-standing goal of seeking peaceful unification of the Korean Peninsula and to cement South Korea as its "invariable principal enemy." He said the new charter must specify North Korea would annex and subjugate the South if another war broke out.Observers say North Korea may launch limited provocations along its tense border with South Korea. But they say the prospects for a full-scale attack by North Korea are dim as it would know its military is outmatched by the U.S. and South Korean forces.___Associated Press writer Mari Yamaguchi in Tokyo contributed to this report.