North Korea launched a long-range ballistic missile toward its eastern waters Wednesday, its neighbors said, two days after the North threatened “shocking” consequences to protest what it called a provocative U.S. reconnaissance activity near its territory.

South Korea's military detected the long-range missile launch from the North’s capital region around 10 a.m., the South's Joint Chiefs of Staff said in a statement. It said South Korea's military bolstered its surveillance posture and maintained readiness in close coordination with the United States.

Japanese Defense Minister Yasukazu Hamada told reporters that the North Korean missile was likely launched on a lofted trajectory, at a steep angle that North Korea typically uses to avoid neighboring countries when it tests long-range missiles.

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Hamada said the missile was expected to land at sea about 550 kilometers (340 miles) east of the coast of the Korean Peninsula outside of the Japanese exclusive economic zone.

North Korea's long-range missile program targets the mainland U.S. Since 2017, North Korea has performed a slew of intercontinental ballistic missile launches as part of its efforts to acquire nuclear-tipped weapons capable of striking major U.S. cities. Some experts say North Korea still has some technologies to master to possess functioning nuclear-armed ICBMs.

Before Wednesday's launch, the North's most recent long-range missile test happened in April, when it launched a solid-fuel ICBM, a type of weapon that experts say is harder to detect and intercept than liquid-fuel weapons.

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Wednesday's launch, the North’s first weapons firing in about a month, came after North Korea earlier this week released a series of statements accusing the United States of flying a military plane close to North Korea to spy on the North.

The United States and South Korea dismissed the North’s accusations and urged it to refrain from any acts or rhetoric that raised animosities.

In a statement Monday night, Kim Yo Jong, the influential sister of North Korean sister Kim Jong Un, warned the United States of “a shocking incident” as she claimed that the U.S. spy plane flew over the North’s eastern exclusive economic zone eight times earlier in the day. She claimed the North scrambled warplanes to chase away the U.S. plane.

In another fiery statement Tuesday, Kim Yo Jong said the U.S. military would experience “a very critical flight” if it continues its illicit, aerial spying activities. The North’s military separately threatened to shoot down U.S. spy planes.

“Kim Yo-jong’s bellicose statement against U.S. surveillance aircraft is part of a North Korean pattern of inflating external threats to rally domestic support and justify weapons tests,” said Leif-Eric Easley, a professor at Ewha University in Seoul. “Pyongyang also times its shows of force to disrupt what it perceives as diplomatic coordination against it, in this case, South Korea and Japan’s leaders meeting during the NATO summit.”

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North Korea has made numerous similar threats over alleged U.S. reconnaissance activities, but its latest statements came amid heightened animosities over North Korea’s barrage of missile tests earlier this year.