South Korea suspended some commercial flights and scrambled military assets to shoot at drones from North Korea that crossed their heavily armed border Monday.

South Korea’s Joint Chiefs of Staff said the military detected multiple “unidentified objects” in the country’s airspace presumed to be unmanned aerial vehicles crossing the border from 10:25 a.m. in Gyeonggi province, which encircles Seoul.

It dispatched fighter jets and military helicopters that fired warning shots toward the objects, JCS said, without saying whether any of the drones had been shot down. The drones flew near Seoul after passing civilian residences and South Korea tried to shoot the aerial vehicles down, Yonhap News Agency reported, citing a government source.

The drones are the first North Korea has sent across the border since June 2017, Yonhap said. They add a new twist to provocations from Pyongyang, which fired two suspected short-range ballistic missiles Friday that added to the record tally of rocket launches under Kim Jong Un this year.

The North Korean leader is finding space to ratchet up tensions and conduct tit-for-tat military moves against the U.S. and its allies as President Joe Biden focuses on Russia’s war in Ukraine. The missile launch came three days after the U.S. sent a bomber and F-22 stealth fighters to the peninsula for joint drills with South Korea.

Kim has called for a meeting of his ruling Workers’ Party at an unspecified date in late December to review economic and political efforts for this year and decide on policy plans for 2023. He has shown no interest in returning to nuclear disarmament talks that have been stalled for almost three years, and has stood firmly to a pledge to never give up his atomic arsenal.

With assistance from Sangmi Cha and Heejin Kim.