The US military removed aircraft from a second airbase in Britain on Monday after receiving a reported threat from Iran. The Wall Street Journal first reported the move, citing people familiar with events, and the story was carried widely on 10 November.

Up to 12 refuelling aircraft were flown out on Monday from RAF Mildenhall to US bases in Germany and Spain. Sky News said 12 aircraft, nine tankers and three Osprey transporters, left Mildenhall on Monday, citing flight tracking sources. Two of the withdrawn tankers diverted to Germany, while several others at the base were moved to Germany and other locations later in the day.

The nature of the threat

The precise nature of the threat to RAF Mildenhall in Suffolk remains under discussion among US officials. The Wall Street Journal reported, quoting a US official, that the base had upgraded its security status to FPCON Charlie, the second-highest defensive threat level, which occurs when intelligence indicates that terrorist action is likely.

A security source said it was likely there was credible intelligence to indicate Iran was preparing to engage in a drone attack targeting Mildenhall. The alleged Iranian threat involved a plan to apparently target the base with kamikaze drones, according to sources quoted in the reports.

The Pentagon did not immediately respond to a request for comment. A spokesperson for the US military's European Command declined to discuss specific force protection measures, noting that various factors can affect them. A US official said the decision to move the aircraft was proactive rather than reactive, adding that the US military is agile to potential threats.

The second base in two months

The move follows an earlier plot against another RAF airbase housing US aircraft at Fairford in September. American aircraft have since been moved elsewhere, and the Mildenhall withdrawal came just weeks after the US removed B-1 bombers from RAF Fairford due to unspecified threats linked to Iran.

That followed a security incident at the base in southwest England in September, which the British prime minister has said Iran's Revolutionary Guards almost certainly directed. Seven people, including a British-Iranian national, were arrested over the alleged plot to target the base, with counter-terrorism police last month charging two of them with national security offences.

RAF Mildenhall hosts the US Air Force's 100th Air Refueling Wing, which includes its Stratotankers, Commando II and Osprey aircraft. As well as KC-135 refuelling aircraft, Mildenhall has C-130J Hercules aircraft operated by the 352nd Special Operations Wing for covert low-level infiltration operations by US special forces.

Flight tracking confirms the move

Flight tracking data analysed by news agencies showed at least 10 refuelling tankers and three Ospreys have left the base since early Monday. Tracking platforms showed one of the refuelling planes was moved to an airbase in Scotland, three went to Moron airbase in Spain and another four to Ramstein airbase in Germany.

Another US transport aircraft that landed at Mildenhall early Tuesday departed shortly after 11 am GMT, according to flight tracking data. The US military said on Tuesday it was taking coordinated and appropriate security steps after the flight tracking data showed the withdrawals.

The reports also said Republican and Democratic leaders in the House and Senate, as well as the leaders of the intelligence committees in both chambers, were briefed on Iran's threats to US interests on Monday as Congress returned to Washington following the midterm elections.