According to the daily Chosun Ilbo, an RC-135W Rivet Joint was "scrambled over the Seoul metropolitan area" after North Korea announced it was testing a new tactical guided missile last week.
"The plane chiefly captures remote signals generated when a ballistic missile is fired," the Seoul-based newspaper said.
The daily said the aircraft has "seldom flown over the Seoul area", but normally remained over the West Sea -- also known as the Yellow Sea -- and nearby areas.
"The last time it was scrambled over Seoul was when the North conducted a series of missile tests in 2017," the report quoted a South Korean military official.
The spy plane flew over Gyeonggi and Gangwon provinces, south of the no-fly zone set up under a cross-border military agreement signed in September last year.
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