North Korea test-fired a suspected ballistic missile Wednesday after warning the US of “shocking” consequences for flying spy planes Pyongyang claimed violated its airspace.

North Korea fired a ballistic missile toward waters off its east coast, South Korea’s Joint Chiefs of Staff said in a text message sent to reporters. The missile appeared to still be in the air more than 20 minutes after its launch, Japanese public broadcaster NHK reported. This could indicate that North Korea fired a long-range rocket.

The last time Kim Jong Un’s regime launched ballistic missiles was about three weeks ago when it fired two short-range rockets shortly after threatening to punish US for holding joint military drills with South Korea.

North Korea Says It Scrambled Warplanes to Ward Off US Aircraft

Kim Yo Jong, the powerful sister of the leader, was cited by Pyongyang’s state media a day earlier as threatening retribution for the flights. South Korea said the aerial reconnaissance aircraft did not violate North Korean airspace.

Prior to the latest launch, Pyongyang had already fired 19 ballistic missiles so far this year, including three intercontinental ballistic missiles designed to deliver a nuclear warhead to the US mainland. The country launched more than 70 ballistic missiles last year, a record for the state.

Kim Jong Un has ignored US calls to return to long-stalled nuclear disarmament talks. But he has been busy modernizing his arsenal of missiles and conducting tests of systems to attack South Korea and Japan, which host the bulk of US military personnel in the region.

The launch came as North Atlantic Treaty Organization leaders gathered 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.

(Adds comment from Japan, NHK report and background on recent events)