SEOUL, South Korea (AP) — North Korea on Monday fired four banned ballistic missiles that flew about 1,000 kilometers (620 miles) on average, with three of them landing in waters that Japan claims as its exclusive economic zone, South Korean and Japanese officials said.

The test-launches appeared to be a reaction to huge U.S.-South Korean military drills that those countries consider routine but that Pyongyang insists are an invasion rehearsal.

It was not immediately clear the exact type of missile fired, but the tests will be viewed as a provocation by the Trump administration, which is working on its policy for North Korea. The New York Times reported over the weekend that the United States still can’t effectively counter Pyongyang’s actions despite efforts to perfect cyber and electronic strikes against North Korea’s missile program.

It’s the third time that North Korean missiles have fallen in the Japanese zone, beginning last August. Japanese leaders see the launches into nearby waters as a growing threat.

U.S. State Department spokesman Mark Toner said, “We remain prepared — and will continue to take steps to increase our readiness — to defend ourselves and our allies from attack, and are prepared to use the full range of capabilities at our disposal against this growing threat.”