Seoul, Jul 11 (IANS): Kim Yo-jong, the sister of North Korean leader Kim Jong-un, on Tuesday warned that spy jets will face a "very critical flight" in case of a repeated illegal intrusion into the Pyongyang's exclusive economic zone, threatening to take military action.

"I have already notified beforehand the counteraction of our army upon authorization. In case of repeated illegal intrusion, the U.S. forces will experience a very critical flight," Kim Yo-jong said in a statement published by the North's official Korean Central News Agency (KCNA).

The warning came hours after she issued a statement late Monday alleging that a US spy aircraft entered North Korea's exclusive economic zone earlier in the day, reports Yonhap News Agency.

Earlier Monday, a spokesperson of the North's Defence Ministry also accused the US spy aircraft of intruding into its airspace recently, threatening that there is no guarantee such aircraft will not be shot down.