North Korea's state media claimed Saturday that the South Korean military's unmanned aerial vehicle violated its airspace this week, calling it a "grave military provocation."

An official from the South Korean military dismissed the claim as "untrue," saying it carried out a "normal operation as planned."

The North's official Korean Central News Agency reported that the South's surveillance plane, called Heron, flew over its western border area four times between 7:46 a.m. and 8:40 p.m. on Friday.

The KCNA said that the alleged violation was grave as it came when the United States brought its four Global Hawk spy drones and some 100 military personnel to Yokoda Air Base in Japan from their base in Guam on the pretext of avoiding a typhoon.

It also blamed the South for escalating military tensions, warning of a "merciless retaliatory response."

In recent weeks, Pyongyang has ratcheted up military tensions through a series of ballistic missile tests, which many observers said indicated it is on course to develop a longer-range missile capable of reaching the U.S. mainland.

On Sunday, the North fired an intermediate-range missile with its leader Kim Jong-un approving its deployment for combat use.

The latest provocation followed the May 14 test of another missile, which experts presumed could have a range of around 5,000 kilometers. (Yonhap)