North Korea's Kim Yo Jong, the powerful sister of leader Kim Jong Un, said on Tuesday that a US military spy plane entered the country's Exclusive Economic Zone eight times on Monday, state media KCNA reported.
Kim also vowed that the US forces will face a "very critical flight" if they continue what it called "illegal intrusion."
Calling the issue "one between the Korean People's Army and the US forces," she told South Korea to refrain from getting involved in a statement.
Kim accuses the US Air Force of intruding into the North's "economic water zone" off the east coast of the Korean peninsula in the sky above the sea 435 km (270 miles) east of Thongchon of Kangwon Province and 276 km southeast of Uljin of North Gyeongsang Province.
North Korea's Exclusive Economic Zone
A country's Exclusive Economic Zone (EEZ) - which extends 200 nautical miles from the 12 nautical-mile territorial zone around the coast - is a right to exploit marine resources within but does not confer sovereignty over the water's surface or the airspace above it.
Tuesday's statement comes after North Korea accused the US of violating its airspace by conducting surveillance flights and warned such flights may be shot down.