South Korea scrambled aircraft and fired warning shots after North Korean drones flew into its airspace on Monday morning.
The response came days after Pyongyang launched two ballistic missiles into the Sea of Japan, in an unprecedented year of weapons tests by the rogue state.
It was not immediately clear if the drones were taken down, but the Yonhap news agency later said South Korean forces fired about 100 shots but failed to shoot any down.
It is the first time North Korean drones have entered South Korean airspace since 2017, when a drone suspected to have been sent by Pyongyang was found crashed south of the border.
South Korean military officials said at the time that the drone had photographed a US missile defence system before crashing.
Officials in Seoul say North Korea has previously touted its drone program and has about 300 of the unmanned vehicles.
In 2014, several suspected North Korean drones were found south of the border, and while experts said they were low-tech, they could still be considered a potential security threat.
Last Friday, North Korea fired two short-range ballistic missiles toward its eastern waters, according to South Korea’s Joint Chiefs of Staff.
It marked the 36th day that North Korea test launched missiles, often firing multiple projectiles each time.
The latest launch was seen as a protest of the South Korean-US joint air drills that Pyongyang views as an invasion rehearsal.
This year, North Korea has conducted an unprecedented number of missile tests in what some experts call an attempt to improve its weapons and pressure rivals to make concessions such as lifting sanctions in future negotiations.
Recently, the North also claimed to have performed major tests needed to acquire its first spy satellite and a more mobile intercontinental ballistic missile capable of reaching the US mainland.
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