U.S. flies spy plane after N. Korea’s test of underwater nuclear attack drone

A U.S. surveillance aircraft flew over South Korea on Monday, aviation trackers showed, on an apparent mission to monitor North Korea following its claimed test of an underwater nuclear attack drone.

The U.S. Air Force’s RC-135W Rivet Joint was spotted in skies above the city of Incheon, just west of Seoul, and the adjacent Gyeonggi Province, Gangwon Province as well as the eastern and western coasts, according to multiple flight trackers.

The RC-135V was dispatched three days after North Korea claimed it tested an underwater nuclear attack drone, Haeil-5-23, in the East Sea in response to the latest joint naval drills involving South Korea, the U.S. and Japan last week.

The U.S. deployment of the advanced spy aircraft is part of its regular intelligence-gathering operations, but its exposing extensive flight routes may be aimed at sending a message of pressure to the North, according to sources.

It is the third known flight this year following two previous ones on Jan. 4 and 17, whose flights were spotted only in inland airspace.

South Korea and the U.S. have stepped up monitoring to detect possible signs of Pyongyang’s provocations as North Korean leader Kim Jong-un has called for stronger war readiness against “unprecedented” acts of U.S.-led confrontations.