SEOUL, South Korea (AP) — North Korea launched at least one short-range ballistic missile off its east coast Monday, South Korea’s military said, a day after the North vowed “offensive and overwhelming” responses to a new U.S. military drill with South Korea and Japan.

The Joint Chiefs of Staff said the missile was launched from North Korea’s southeastern town of Jangyon at 5:05 a.m. It said an additional, unidentified ballistic missile launch trajectory was detected 10 minutes later, a suggestion that North Korea might have performed two missile launches.

The Joint Chiefs of Staff said South Korea’s military has boosted its surveillance posture and is closely exchanging related information with the United States and Japan.

The launch came two days after South Korea, the U.S. and Japan ended their new multidomain trilateral drills in the region. In recent years, the three countries have been expanding their trilateral security partnership to better cope with North Korea’s evolving nuclear threats and China’s increasing assertiveness in the region.

The “Freedom Edge” drill was meant to increase the sophistication of previous exercises with simultaneous air and naval drills geared toward improving joint ballistic-missile defense, anti-submarine warfare, surveillance and other skills and capabilities. The three-day drill involved a U.S. aircraft carrier as well as destroyers, fighter jets and helicopters from the three countries.

On Sunday, North Korea’s Foreign Ministry issued a lengthy statement strongly denouncing the “Freedom Edge” drill, calling it an Asian version of NATO. It said the drill openly destroyed the security environment on the Korean Peninsula and contained a U.S. intention to lay siege to China and exert pressure on Russia.