The powerful sister of North Korean leader Kim Jong-un on Monday warned the United States of a "decisive response" if its military enters the regime's exclusive economic zone(EEZ) again.

Kim Yo-jong issued the warning in a statement carried by the North's official Korean Central News Agency(KCNA) at around 9 p.m. Monday.

Kim accused the U.S. of violating the country's EEZ off the east coast by conducting surveillance flights over the sea east of Tongchon in Kangwon Province and Uljin in North Gyeongsang Province from 5 a.m. Monday.

Kim said that North Korean warplanes chased away the U.S. spy plane, but it again violated the country’s maritime demarcation line and economic water zone in the skies above Goseong in Gangwon Province at around 8:50 a.m.

Kim warned that the North will take decisive action if U.S. aircraft violates its economic water zone again.

The designation of an EEZ – which extends 200 nautical miles from the 12 nautical-mile territorial apron around the coast – permits a country to capitalize on marine sources within but does not confer sovereignty over the waters or airspace.

Earlier on Monday, North Korea's defense ministry issued a statement accusing the U.S. of flying spy planes into its “inviolable airspace” and warning that approaching aircraft might be shot down.