The US military removed aircraft from a second airbase in Britain on Monday after a threat from Iran.
The withdrawal comes weeks after Washington removed its bombers from RAF Fairford airbase over a suspected Iran-linked security incident.
Two US refuelling tankers using the RAF Mildenhall military base were diverted to Germany on Monday, while several other tankers at the base were moved to Germany and other locations later in the day, The Wall Street Journal reported. It added that the precise nature of the threat to RAF Mildenhall remains under discussion among US officials.
The US upgraded the security status at RAF Mildenhall and RAF Lakenheath to "FPCON Charlie", the report quoted a US official as saying.
Force Protection Condition Charlie is the second-highest defensive threat level in the US Department of Defence's security system and occurs when intelligence indicates that a form of terrorist action is likely.
“We do not routinely comment on the activity of other nations. Aircraft and other assets move regularly according to operational requirements,” a British Ministry of Defence representative said.
A US Air Force representative declined to provide details about the movement of assets, but said US aircraft rotated between sites for a variety of reasons.
Five men were arrested outside RAF Fairford airbase in south-western England in September over a security incident, with two others arrested later on suspicion of assisting Iranian intelligence.
The circumstances of the incident, which remain largely unexplained, attracted huge international attention, coming at a time of heightened concern about the security implications for western states of the Iran war, and prompted the US to remove its B-1 bombers from the Fairford airbase on security grounds.
RAF Fairford had been used by US bombers to carry out strikes on Iran.
British Prime Minister Andy Burnham said last month that the activity at RAF Fairford was likely to have been co-ordinated in Iran. While Tehran's ambassador to Britain has denied accusations that it was involved in any plot against the airbase, Iran's Islamic Revolutionary Guard Corps said in July that the Fairford base, and any other military site used to launch attacks against Iran, were legitimate targets.
Iran has also been blamed for sabotage attacks on supermarket freezers and blood banks across Europe in the past week.
