North Korea fired an unspecified ballistic missile toward the east coast on Saturday, South Korea’s Joint Chiefs of Staff said, marking Pyongyang’s fourth launch in a week as it ratchets up tension in the Korean peninsula, according to Reuters.

The launch comes after the U.S. and South Korea held the Ulchi Freedom Shield, the biggest joint military drill in about five years, and after U.S. Vice President Kamala Harris visited South Korea this week.