The sister of North Korean leader Kim Jong-un threatened Tuesday that the US military will face a "very critical flight" in case of a "repeated illegal intrusion," the latest in a string of warnings against US spy planes allegedly violating its airspace.

The warning by Kim Yo-jong, carried by the North's official Korean Central News Agency (KCNA), 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.

"I have already notified beforehand the counteraction of our army upon authorization. In case of repeated illegal intrusion, the US forces will experience a very critical flight," Kim said.

The Pentagon said that the US military is bound by international law.

"These are just accusations," said a spokeswoman for the US Department of Defense, Sabrina Singh.

US State Department spokesman Matthew Miller urged North Korea to "refrain from escalatory actions," reiterating its call to "engage in serious and sustainable diplomacy." North Korea accused the US Air Force of violating the airspace of North Koreas "economic water zone" off the eastern coast of the Korean peninsula.

North Koreas 200-nautical-mile exclusive economic zone gives it the right to exploit its marine resources, but not sovereignty over the surface of the waters or the airspace above it.

Source: Qatar News Agency