London (AFP) - The US military said Tuesday it was taking “coordinated and appropriate” security steps after flight-tracking data showed it had withdrawn at least a dozen aircraft from a second British airbase.

The removal on Monday of the American refuelling tankers and other aircraft from Mildenhall Royal Air Force (RAF) base in eastern England followed a threat from Iran, the Wall Street Journal (WSJ) reported.

Citing people familiar with events, the newspaper said the “precise nature” of the Iranian threat remained “under discussion” among United States officials.

A spokesperson for the US military’s European Command (EUCOM) declined to discuss “specific force protection measures”, noting various factors can affect them.

“In close partnership with our host nation allies, both RAF Mildenhall and RAF Lakenheath remain vigilant,” the spokesperson added, referring to another nearby British airbase.

“Together, we are taking coordinated and appropriate actions to ensure the safety and security of our US service members, US and host nation civilians, contractors, and all of our families.”

The Mildenhall withdrawals came just weeks after the US removed B-1 bombers from another British base, RAF Fairford, due to what President Donald Trump said were unspecified threats linked to Iran.

That followed a security incident at the base in southwest England in September, which Prime Minister Andy Burnham 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.

- ‘Firm and quick’ -

Trump on Monday said Washington was “seeing positive momentum toward an end” to the conflict with Iran, which began after he launched strikes on the country in late February alongside Israel.

Mildenhall hosts the US Air Force’s 100th Air Refueling Wing, which includes its Stratotankers, Commando II and Osprey multi-purpose aircrafts.

At least 10 refuelling tankers and three Ospreys have left the base since early Monday, according to flight-tracking data analysed by AFP.

Tracking platforms FlightRadar24 and AirNav 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.

The Ospreys were moved to nearby Lakenheath, 10 kilometres (six miles) from Mildenhall.

Another US transport aircraft that landed at Mildenhall early Tuesday – the only aircraft to arrive there in the past 24 hours – departed shortly after 1100 GMT, according to flight-tracking data.

A British defence ministry spokesman told AFP: “We do not routinely comment on the activity of other nations.

“Aircraft and other assets move regularly according to operational requirements.”

Burnham’s official spokesperson insisted British airbases were safe.

“Protection of our bases, both in the UK and across the world, is a top priority,” he told reporters at a daily briefing.

“We work closely with the police and our allies to protect our sites,” he said, adding Britain kept “security measures under constant review to protect our national security”.