US refueling tankers moved to Germany due to unspecified Iran threat, source says

A U.S. official said the U.S. takes "proactive measures" to ensure safety.

The U.S. moved refueling tankers based at RAF Mildenhall in the United Kingdom to a base in Germany because of an unspecified Iran threat, according to a source familiar with the matter. 

The force protection levels at RAF Mildenhall and RAF Lakenheath were increased to FPCON Charlie, according to the source. 

"We take proactive measures to ensure our aircraft, our people, and our installations remain safe and secure," a U.S. official told ABC News.

The Wall Street Journal was first to report on why the aircraft had been moved away from the bases. The War Zone was first to report that the security postures at the bases had been increased.

"U.S. Air Force aircraft rotate between installations and operating locations for a variety of reasons including training and real world requirements," a U.S. Air Force spokesperson said in a statement. "U.S. military aircraft are hosted in accordance with access, basing, and overflight agreements with our Allies and partners. Due to operations security, we will not provide further information on movement of assets."