One of the three ballistic missiles recently test-fired by North Korea likely exploded in the air during its initial stage of flight due to some sort of malfunction, military officials familiar with the matter said Friday.

According to military sources, one of the three missiles blew up at an altitude of less than 30 kilometers, though two others flew 500-600 km from Hwangju, south of Pyongyang, across the communist country before hitting the East Sea early this week.

"Pyongyang's claim to have used the missile launches to test a nuclear detonator device (on all the three missiles) could be false," a military official said. 

On Tuesday, North Korea test-fired three ballistic missiles in an apparent "armed protest" against South Korea's decision early this month to deploy an advanced U.S. anti-missile system in the country to counter growing threats from the North.

Back then, it was believed Pyongyang test-fired one mid-range Rodong and two shorter-range Scud missiles. But South Korea's military corrected the count to two Rodongs and one Scud.

On Wednesday, Pyongyang said it conducted the missile launch drill with the aim of practicing pre-emptive strikes against South Korean ports and airfields. (Yonhap)