The U.S. Air Force's RC-135 surveillance plane. Wikipedia

The United States flew a RC-135S surveillance plane over South Korea's East Sea, an aviation tracker said Tuesday, on an apparent mission to collect intelligence regarding North Korea.

The RC-135S Cobra Ball aircraft departed Kadena Air Base in Japan's Okinawa and flew over the East Sea earlier in the day, Aircraft Spots said in a Twitter post.

The surveillance aircraft last made a similar flight over the region in early October.

As one of America's major intelligence-gathering assets, the aircraft collects data regarding missile launches, such as the movement of transporter erector launcher (TEL) vehicles and electronic signals, a military source here said.

The deployment came a week after North Korea tested a "super-large" multiple rocket launcher as the latest in a series of test-firings of projectiles, including new types of ballistic missiles. On Oct. 2, North Korea also test-fired a new type of SLBM, the Pukguksong-3.

The South Korean military has said it is monitoring the situation in case the North conducts additional launches and is maintaining a readiness posture.

During a parliamentary audit Monday, the National Intelligence Service (NIS) said North Korea could test-fire a missile from its new submarine being built at the Sinpo shipyard on its east coast. The submarine is estimated to be in the final stages of construction. (Yonhap)