North Korea launched a short-range ballistic missile toward the sea on Sunday, its neighbors said, ramping up testing activities in response to ongoing U.S.-South Korean military drills that it views as an invasion rehearsal.

The North’s continuation of missile tests showed its determination not to back down, despite the U.S.-South Korea exercises, which are the biggest of their kind in years. But many experts say the tests are also part of North Korea’s bigger objective to expand its weapons arsenal, win international recognition as a nuclear state and get international sanctions lifted.

The missile launched from the North’s northwestern Tongchangri area flew across the country before it landed in the waters off its east coast, according to South Korean and Japanese assessments. They said the missile traveled a distance of about 500 miles, a range that suggests the weapon could target South Korea.