A U.S. spy aircraft flew over the Korean Peninsula for an apparent mission to surveil North Korea on Monday, according to aviation data, amid Pentagon policy chief Elbridge Colby’s visit to Seoul.

The Air Force’s RC-135U Combat Sent (64-14847) departed Kadena Air Base in Okinawa at around 8 p.m. KST on Monday and began patrols at 9:43 p.m., according to Flightradar24 tracking data.

The aircraft made several loops across South Korea, flying south of Seoul from the Yellow Sea to the East Sea (Sea of Japan) before returning to its base in Okinawa.