North Korea said it scrambled warplanes to ward off a US spy plane in its exclusive economic zone and raised the possibility of “shocking” consequences if the incursions persist.

Kim Yo Jong, the powerful sister of leader Kim Jong Un, said early Tuesday in a statement carried by the Korean Central News Agency that that the US aircraft “retreated” when the North Korean air force sent up a sortie of planes.

“The intrusion into the DPRK’s 200-nautical mile economic water zone by the reconnaissance asset of the hostile country ... is clearly a grave encroachment upon the sovereignty and security of the DPRK,” Kim said, referring to North Korea by its formal name.

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Her comments came hours after Pyongyang claimed US drones and spy planes flew for eight straight days along its coasts, with aircraft repeatedly violating its airspace.

South Korea’s military disputed those accusations, saying the aerial reconnaissance aircraft did not violate North Korean airspace. It said Pyongyang has willfully stirred tensions by launching threats over “normal flight activities” over international waters. It urged the North to immediately cease such actions.

Kim Yo Jong also criticized South Korea for defending the US activities. “As regards the provocation by the US forces, the military of the ‘ROK’ again impudently took the lead in denying the encroachment on the DPRK’s sovereignty, while shamelessly asserting that it was a ‘normal flight.’”

The latest flare-up in tensions on the peninsula came as North Atlantic Treaty Organization leaders prepare to gather in Lithuania for their annual summit. The leaders of Japan, South Korea, Australia and New Zealand will attend in a bid to bolster awareness of security threats in the Asia-Pacific.

Speaking at a forum in Seoul on Monday, John Weidner, chief of staff at the US Forces Korea, reaffirmed Washington’s commitment to enhancing the “regular visibility” of powerful military assets in South Korea, referring to the “upcoming visit” of a US nuclear ballistic missile submarine, Yonhap reported.

“The US will enhance regular visibility of strategic assets to the Korean Peninsula as evidenced by the upcoming visit of a US nuclear ballistic missile submarine to the ROK,” Weidner said, referring to South Korea by its formal name.

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