The powerful sister of North Korean leader Kim Jong-un has warned that U.S. forces will face a "very critical flight" if they continue what it called "illegal intrusion."

In a statement carried by the North’s official Korean Central News Agency(KCNA) early Tuesday, Kim Yo-jong issued the warning as she claimed that a U.S. spy aircraft entered the country’s exclusive economic zone(EEZ) eight times on Monday.

Kim accused U.S. reconnaissance aircraft of intruding into the zone over waters 435 kilometers east of Tongchon of Kangwon Province and 276 kilometers southeast of Uljin County in North Gyeongsang Province between 5:15 a.m. and 1:30 p.m. Monday.

Kim then warned that the U.S. military will experience a "very critical flight" in case of a repeated illegal intrusion.

She also told South Korea to refrain from getting involved, saying that the matter concerns the North’s Korean People’s Army and the U.S. military.

The warning came nine hours after she issued a similar statement accusing a U.S. spy aircraft of entering North Korean airspace within its EEZ.