The U.S. military has reportedly flown spy planes over the Korean Peninsula on an apparent mission to monitor North Korea.

According to the aviation tracking website Aircraft Spots on Tuesday, the U.S. Air Force's E-8C and Navy's P-3C were spotted in skies above South Korea.

It did not elaborate on the flight time of the aircraft, but the flights are thought to have occurred on Tuesday morning.

On Monday, the U.S. Air Force's RC-135W Rivet Joint was seen operating above the peninsula. 

The U.S. military appears to be boosting its surveillance of North Korea's movements after the North fired what appeared to be short-range cruise missiles off its east coast last week.