ENGLAND -- The United States has evacuated American military aircraft from a military base in England on Monday following a threat from Iran that was deemed credible, according to a person familiar with the intelligence that prompted the evacuation.

The source declined to detail the nature of the threat to the base, RAF Mildenhall, but said that the US intelligence community has in recent weeks picked up a wide range of “varied, extensive, and specific” plots being discussed by the Iranians against American targets.

It is unclear whether the Iranians actually have the capabilities needed to act on the threats, however, which range from drone attacks on US bases to assassination plots. Several threats were also made against targets inside the United States, the source said.

“The Iranians clearly had specific targets and methods in mind,” the source told CNN.

CNN has reached out to the Iranian Embassy in London for comment on the allegations.

A US official said aircraft were removed from the base as a “temporary relocation,” but declined to comment on any threat.

A spokesperson for British Prime Minister Andy Burnham told CNN that the UK is in “constant communication with” the US, “sharing intelligence and accessing threats together.”

“Aircraft and other assets move regularly according to operational requirements,” the spokesperson said. “The protection of our bases, both in the UK and across the world, is a top priority.”

The US aircraft evacuations were first reported by The Wall Street Journal.

Flight tracking data analyzed by CNN shows that 10 US refueling aircraft were relocated away from RAF Mildenhall on Monday. Four of those KC-135 Stratotankers went to Germany’s Spangdahlem Air Base, one to Germany’s Ramstein Air Base, four to Spain’s Morón Air Base and one to Scotland’s Glasgow Prestwick airport.

The United States also upgraded the security threat level at RAF Mildenhall and another airbase RAF Lakenheath to “FPCON Charlie,” according to The WSJ and the defense industry publication The War Zone, citing a US official on Monday. That threat level – the second-highest level in the Pentagon’s force protection system – indicates that some form of terrorist action or targeting action is likely.

Another American official, from the US European Command, said that “US Air Force aircraft rotate between installations and operating locations for a variety of reasons including training and real world requirements… Due to operations security, we will not provide further information on movement of assets.”

A UK Ministry of Defense spokesperson said that they “do not routinely comment on the activity of other nations.” The spokesperson added that “aircraft and other assets move regularly according to operational requirements.”

The movement of the planes comes after another Iran-linked threat last month to another military base in England, RAF Fairford.

RAF Fairford had been used by US B-1 bombers to carry out strikes on Iran, but they were withdrawn on security grounds shortly after five men were arrested outside the base in the early hours of September 27.

British prosecutors charged two British nationals under the National Security Act in relation to the incident outside RAF Fairford airbase, with police saying the two were suspected of assisting Iran.

This story has been updated with additional developments.

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