North Korea said Thursday an unidentified flying object at which South Korea's military fired rounds of warning shots this week was actually a "flock of birds," not a balloon carrying propaganda leaflets as Seoul has claimed.

A spokesman of the General Staff of the North's Korean People's Army, through the country's official news agency, criticized South Korea's action as "another armed provocation" in the area along the Military Demarcation Line.

The refutation came a day after South Korea revised its initial claim that the object, which crossed the border from North Korea on Tuesday, may have been a drone, saying it was most likely a balloon.

The unnamed spokesman said South Korea's firing of bullets was aimed at stirring up anti-Pyongyang sentiment, according to the Korean Central News Agency.

KCNA also quoted him as saying that South Korea's military fired more than 450 machine gun bullets into its territory, far more than the roughly 90 shots Seoul claims to have fired.

The incident came amid high tensions around their heavily armed border areas and on the Korean Peninsula as a whole following a series of ballistic missile launches by North Korea in defiance of international warnings.