PYONGYANG, May 27 (Xinhua) -- The Democratic People's Republic of Korea (DPRK) Saturday accused South Korea of drone intrusions into its territorial space, two days after Seoul said a suspected DPRK drone flew across the military demarcation line.

The Korean Central News Agency said a "Heron" spy drone intruded deep into the territorial space of the DPRK above the waters near the border four times Friday.

"Such grave military provocation was committed when the U.S. imperialists forward-deployed four 'Global Hawks' (spy planes) and over 100 pilots at the Yokoda air base of Japan, near the DPRK, from Guam under the pretext of escaping from a typhoon," said the report.

The report said the areas intruded by the drone were "hot spot waters" where the two sides dispute over demarcation lines and over which the DPRK and South Korean troops clashed several times in the past.

South Korea said Thursday a suspected DPRK drone flew across the military demarcation line separating the north and south parts of the peninsula and its troops opened fire on it.

DPRK said the flying subject was "a flock of birds" and called the accusation "nothing but mental derangement."