A man has been arrested after driving through a military checkpoint, getting close to an aircraft at a base in Suffolk used by the US Air Force.
Shots were fired by US personnel before the 44-year-old British man was overcome by staff at RAF Mildenhall.
The base was temporarily put into lockdown as Suffolk police responded to reports of what they called a "significant incident".
Police said the incident was being treated as trespass, not terrorism.
Supt Kim Warner, from Suffolk Police, said the man, who suffered cuts and bruises, was arrested after a "short pursuit" and his vehicle was stopped by US security services.
There was "no obvious motive at this stage", he said, adding there was no wider threat to the public or the base and police were not looking for anyone else.
The vehicle was brought to a halt close to a US plane, an Osprey, and it was not thought there was "any significant damage" to the vehicle or the aircraft, Supt Warner said.
Suffolk Police was notified about a breach of security at about 13:40 GMT.
"Shots were fired by US security, I don't know how many, but I do know that shots were fired," Supt Warner said.
"It would be fair to say some of the minor injuries were probably as a result of him being apprehended," he added.
The superintendent said there would now be an internal investigation by the US airbase into why guns were discharged.
Police are continuing to deal with an ongoing incident at RAF Mildenhall, it is considered that there is no wider threat to the public or occupants on the base. One man has been arrested and police are not looking for anyone else on the site.— Suffolk Police (@SuffolkPolice) December 18, 2017
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RAF Mildenhall is protected by Ministry of Defence police and US armed guards.
The US Air Force said in a statement it was continuing to work with local authorities.
The base is used as a transport hub by the US and is home to a fleet of refuelling aircraft and special operations forces.
It has about 3,200 military personnel, with 400 to 500 UK civilian staff employed there.
The base was one of 56 MoD sites earmarked for closure.
However, the US Air Force said in September it was delaying plans to relocate its operations to a base in Germany until 2024.
RAF Mildenhall has previously been a potential target for a terror attack against US military personnel.
In May 2016, Junead Khan was given a life sentence for preparing terrorist acts after a court heard how he used his job as a delivery driver to gather information about the base.
'Rules of engagement'
Alex Dunlop, BBC Look East Defence reporter
It's highly unusual for shots to be fired by US personnel. That said, in the past few years security has been stepped up at the US base, which now has a much tighter perimeter.
You can't just drive into the base, you have to go through what's called the '"shed" - your car is checked and you have to go through lots of tight security measures.
RAF Mildenhall is essentially a little piece of America, with more than 3,000 US personnel based here, and there's very close co-operation between the American military police and the British civilian police.
US bases here are governed by the Status of Forces Act so there are very clear rules of engagement here, with certain protocols in place when it come to the discharge of firearms.
US personnel are allowed to fire guns, but these rules of engagement are not made public because of security considerations.
There will undoubtedly be a conversation as a result of this incident between the Pentagon and the Ministry of Defence as to exactly what happened here and why guns were fired.