The US Air Force said security forces responded to “suspected unauthorized drone activity” over England’s RAF Lakenheath on Friday evening, with no personnel, aircraft or infrastructure affected, while the UK Ministry of Defence said the incident was “now resolved” as authorities investigated. By Saturday morning, another 100th Air Refueling Wing KC-135 tanker departed neighboring RAF Mildenhall for Moron Air Base in Spain before relocating to Spangdahlem Air Base in Germany, bringing the total number of aircraft evacuated from Mildenhall since Monday to 18 as a second tanker’s departure was delayed.

During Friday night’s alert, locals recorded warning sirens sounding around the bases, and separate sources reported that Force Protection Condition Delta, the highest of the five US military security levels reserved for an ongoing or imminent terrorist attack, was activated for more than an hour at one or more of the installations. The drone incident followed a weeklong dispersal from Mildenhall that began Monday after US intelligence picked up what a person familiar with the matter told CNN were “varied, extensive, and specific” Iranian plots against US targets, prompting the Pentagon to raise security at Mildenhall and Lakenheath to FPCON Charlie and move 12 based KC-135 tankers, two transient tankers and three CV-22B Ospreys to bases in Germany, Spain, Scotland and Lakenheath.