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

According to the source, the move came in reaction to huge military drills by Washington and Seoul that Pyongyang insists are an invasion rehearsal.

U.S. national security adviser H.R. McMaster and senior South Korean presidential official Kim Kwan-jin held a phone conversation after the missile firings. The two condemned the launches and agreed to boost cooperation to get the North to face more effective sanctions and pressure, according to South Korea's presidential office.

Seoul and Washington call their military drills on the Korean Peninsula, which remains in a technical state of war because the 1950-53 Korean War ended with an armistice and not a peace treaty, defensive and routine.

The agency reminds that Pyongyang has staged a series of missile test-launches of various ranges in recent months, including a new intermediate-range missile in February; it also conducted two nuclear tests last year.