The live-fire drills, involving a South Korean RQ-4B Global Hawk surveillance drone and a US MQ-9 Reaper attack drone, took place at an unspecified location in South Korea, in an apparent show of the allies' military capabilities against North Korean threats, Yonhap news agency reported.

The drills took place under a scenario of striking the origin of an enemy provocation, with the South Korean drone collecting data on simulated targets and sharing it with the U.S. unmanned aircraft, according to the Air Force.

Once the Reaper received the information, the unmanned aircraft released a GBU-38 joint direct attack munition to accurately strike the target, it said.

A military source said the two sides hadn't planned to publicise the drills, but decided to do so in a warning against the North after its ICBM launch.

Earlier in the day, the North said it had successfully launched the new Hwasong-19 ICBM the previous day, which the South's military assessed to be the country's largest long-range missile yet.