What does a raised threat level mean for US airbases in Suffolk?

Five people are under investigation following reports of suspicious vehicles outside RAF Fairford, prompting a higher security level at US airbases across the country - including in Suffolk. What does this mean for Lakenheath and Mildenhall?

A major incident was declared and dozens of homes were evacuated after police were alerted to three vehicles near the Gloucestershire base - used by the US - in the early hours of Sunday.

Five men from London were held by police on suspicion of explosive and terrorism offences and later bailed.

Counter-terror police said the men remained under investigation and their release was "subject to stringent conditions on their movement and contact with others".

The US's response was to increase the state of alert to "Charlie" - the second highest alert level - at their bases in Lakenheath, which houses fighter jets, and Mildenhall, which is mainly used as a base for refuelling tankers.

Charlie alert is usually an indication an incident has happened or intelligence suggests there could be a potential attack.

But there were few visible signs of the raised alert at the Suffolk bases on Monday. However, two large armoured vehicles were placed at the front entrance of Lakenheath, with armed personnel checking arrivals.

Another armoured truck, identified as an Oshkosh Joint Light Tactical Vehicle, was positioned in front of a gate leading to the runway.

The US has refused to comment.

The base has been used as a forward operating location by the US Air Force (USAF) for decades.

In recent months, US bombers have taken off from the base for the Middle East, after the UK approved a US request to use it for defensive strikes on Iran.

In July, Iran said "any base used for aggression against Iranian territory constitutes a legitimate target for our forces".

The site houses F-35 and F-15E fighter aircraft as part of the 48th Fighter Wing.

At least two of its aircraft have been recently shot down, including one in Iran and one in a friendly fire incident over Kuwait.

USAF would not comment on the state of alert and specific force protection measures, but added it would take measures to ensure the safety of its service members.

At Mildenhall, the BBC understands the threat level has also been raised to Charlie.

Like Lakenheath, it has been used as a staging area for aircraft and material bound for the Middle East.

It is also home to air refuelling tankers, which were forward deployed to the region during operations against Iran.

There were no obvious signs of increased security or alerts on Monday, although personnel were spotted enjoying a barbecue.

The base said: "We are aware of the reporting, for operational security reasons we will not discuss specific force protection measures."

Max Khan, from Mersea Island in Essex, was one of the plane spotters gathered near the Lakenheath site on Monday.

He described the events at RAF Fairford as "scary", and believed "US airbases in the UK are potential targets".

"Us as spectators need to be aware of it as well and help out," he said.

"Any suspicious activity needs to be notified to the police and local authorities."

Fellow spotter Chris Braycotton, from Staffordshire, agreed, adding: "You would contact someone, the police or 999 or whoever."

Dave Hawker, from Mumford in Norfolk, described what he called "a security truck" being positioned at the gate, but said so far he had seen "nothing out of the ordinary".

Meanwhile, in the town of Brandon, less than two miles (3.2km) down the road from Lakenheath, locals seemed unperturbed by the increased state of alert.

One man said he had lived next door to the site for 79 years.

"I'm conscious of what's going on, but I don't think the risk is any greater at the moment than it is under normal circumstances," he said.

Another said they felt safer living closer to the base, but one woman said it had brought the issue closer to home.

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