North Korea accused US spy planes of violating its air space and threatened to shoot them down, ramping up tensions just before NATO leaders meet this week in Lithuania for their annual summit.

A spokesman for North Korea’s Defense Ministry said the US was engaging in “the most undisguised nuclear blackmail” by planning to bring a nuclear-armed submarine to the peninsula and conducting “hostile espionage activities” by flying spy planes off its east and west coasts, the state’s Korean Central News Agency reported Monday.

North Korea claimed that drones and spy planes flew for eight straight days along its coasts, with aircraft violating its airspace. “There is no guarantee that such shocking accident as downing of the US Air Force strategic reconnaissance plane will not happen,” it quoted the spokesman as saying.

It added that Pyongyang will take actions to prevent Washington’s “reckless acts.”

Kim Jong Un’s regime has at times fired off ballistic missiles in a show of anger shortly after making threats. Last month, it launched two short-range nuclear-capable rockets just minutes after KCNA issued a dispatch from a Defense Ministry spokesman denouncing joint US-South Korean military exercises and threatening retaliation.

The latest threats stoke concerns about North Korea as South Korean President Yoon Suk Yeol attends the North Atlantic Treaty Organization Summit. Yoon said in an interview with the Associated Press that he will seek help from NATO leaders on how to deter Pyongyang from increasings its atomic ambitions.

South Korea is not a NATO member but Yoon and other leaders will be attending as the bloc and its partners focus attention on support of Ukraine.

The US has flown aerial reconnaissance flights near North Korea for decades and has a network of spy satellites watching its major facilities. South Korea’s Defense Ministry and US Forces Korea didn’t immediately respond to requests for comment.

Yoon and President Joe Biden at a summit in April in Washington agreed to deploy more US nuclear assets to the region. The American president warned Kim that if he conducted a nuclear strike, it would mean the end of his regime.

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The US in June sent a nuclear-powered, guided-missile submarine to South Korea for the first time in six years in a show of force meant to deter North Korea from military strikes. It plans to send another one soon, Yonhap News agency reported.

North Korea has fired off more than 90 ballistic missiles over the past 18 months as Kim rolls out new weapons to deliver a nuclear attack on the US mainland and America’s key allies in the region, South Korea and Japan.

--With assistance from Shinhye Kang, Eunkyung Seo and Seyoon Kim.