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.

The statement said North Korea will “firmly defend the sovereignty, security and interests of the state and peace in the region through offensive and overwhelming countermeasures.”

Monday’s launch was the North’s first weapons firing in five days. On Wednesday, North Korea launched what it called a multiwarhead missile in the first known launch of a developmental, advanced weapon meant to defeat U.S. and South Korean missile defenses. North Korea said the launch was successful, but South Korea dismissed the North’s claim as deception to cover up a failed launch.

In recent weeks, North Korea has also floated numerous trash-carrying balloons toward South Korea in what it has described as a tit-for-tat response to South Korean activists sending political leaflets via their own balloons. South Korea responded by briefly resuming its anti-Pyongyang frontline propaganda broadcasts for the first time in years.

In mid-June, North Korean leader Kim Jong Un and Russian President Vladimir Putin struck a deal vowing mutual defense assistance if either is attacked. Observers say the pact could embolden Kim to launch more provocations at South Korea. The U.S., South Korea and others believe Pyongyang has been supplying conventional weapons to Russia for its war against Ukraine in return for military and economic assistance.

Meanwhile, North Korea opened a key ruling party meeting Friday to determine what it called “important, immediate issues” related to works to further enhance Korean-style socialism. On the meeting’s second day, North Korea's leader spoke about “some deviations obstructing” efforts to improve the country's economic status and unspecified important tasks for resolving immediate policy issues, North Korea’s state media reported Sunday.