(Bloomberg) — North Korea fired multiple cruise missiles into waters off its west coast, stepping up tensions after leader Kim Jong Un said he plans to boost the country’s nuclear-strike capabilities.

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South Korea’s Joint Chiefs of Staff said it detected multiple cruise missiles fired at about 7 a.m. Wednesday and was coordinating with its ally the US to monitor for further activities by North Korea. It did not provide more details on the launches.

North Korea this month fired an intermediate-range ballistic missile designed to hit US bases in Asia for its first such launch of 2024. Pyongyang also criticized joint naval drills among the US, South Korea and Japan held in international waters off the peninsula.

Read: North Korea Test-Fires Its First Ballistic Missile of 2024

North Korea said the previous launch was of a “hypersonic” ballistic missile, indicating it deployed a reentry vehicle that could hold a warhead and maneuver at high speeds. The US, South Korea and Japan said they were analyzing the launch.

North Korea has bristled at joint military exercises for decades, calling them a prelude to an invasion and nuclear war. Although North Korea is barred by UN Security Council resolutions from testing ballistic missiles, it faces no such prohibitions on cruise missiles.

Ballistic missiles fly in an arched trajectory at supersonic speeds and are unpowered on descent. Cruise missiles travel at subsonic speeds and can fly at low altitudes. They are maneuverable, making them harder to detect and intercept.

–With assistance from Shinhye Kang.

(Updates with details.)

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