North Korea every month lists the number of "cases of aerial espionage against the DPRK" by the "U.S. imperialists." The latest monthly total was more than 180 cases, including flights by "U-2 and RC-135 ...for intensively spying on major strategic targets and military installations," RC-7B and RC-12, and, "from Mar. 25 to 31 ...an overseas-based E-3 ...on a mission to command more than 2,000 fighters involved in "RSOI" and "Foal Eagle" joint military exercises for aggression and [to] spy on the areas of the north."
As these are pretty standard monthly reports (which international media seems to forget every month that they reprint them as if there is an imminent crisis), I thought I'd just append some links to see and read about the aircraft in question.
RC-135 Rivet Joint