North Korea test-fired two ballistic missiles Monday but one of them possibly flew abnormally, South Korea's military said, a day after the North vowed "offensive and overwhelming" responses to protest a new U.S. military drill with South Korea and Japan.

The Joint Chiefs of Staff said in a statement the missiles were launched 10 minutes apart in a northeasterly direction from the town of Jangyon in southeastern North Korea.

It said the first missile flew 370 miles and the second missile 75 miles, but didn't say where they landed. North Korea typically test-fires missiles toward its eastern waters, but the second missile's flight distance was too short to reach those waters.

Joint Chiefs of Staff spokesperson Lee Sung Joon later told a briefing the second missile suffered a possible abnormal flight during the initial stage of its flight. He said if the missile exploded, its debris would likely have scattered on the ground though no damages were immediately reported. Lee said additional analysis of the second missile launch was underway.

South Korean media, citing unidentified South Korean military sources, reported that it was highly likely the second missile crashed in an inland area of the North. The reports said the first missile landed in the waters off the North's eastern city of Chongjin.

The Joint Chiefs of Staff condemned the North's launches as a provocation that poses a serious threat to peace on the Korean Peninsula. It said South Korea maintains a firm readiness to repel any provocations by North Korea in conjunction with the military alliance with the United States.

The launch came two days after South Korea, the U.S. and Japan ended their new multidomain trilateral drills. The "Freedom Edge" drill drew a U.S. aircraft carrier and destroyers, fighter jets and helicopters from the three countries, and the three countries practiced missile defense, anti-submarine and maritime interdiction drills.

On Sunday, North Korea's Foreign Ministry issued a lengthy statement strongly denouncing the U.S., South Korea and Japan over their three-way drill. It called the drill an Asian version of NATO that openly destroys the security environment on the Korean Peninsula and contained a U.S. intention to exert pressure on Russia and lay siege to China.

The North's Foreign Ministry said it 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. Last 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.

Both launches came after Russian President Vladimir Putin and North Korean leader Kim Jong Un signed a comprehensive strategic partnership agreement during a summit in Pyongyang in a bid to expand their economic and military cooperation and cement a united front against Washington.

In recent weeks, North Korea has 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.

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 session Saturday, Kim Jong Un spoke about "some deviations obstructing" the county's efforts to improve its economic status and unspecified important tasks for resolving immediate policy issues, North Korea's state media reported Sunday.

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