Shots were fired by US service personnel and a suspect was arrested after a disturbance at RAF Mildenhall but police have not yet confirmed if the incident is being treated as terrorist-related.
Suffolk Constabulary confirmed the arrest as the base, which is used by the US Air Force, was put on lockdown amid reports of a car being rammed into a checkpoint.
The force said the suspect had been taken into custody.
He was said to have suffered cuts and bruises during the incident, which happened at around 1pm on Monday.
MORE: Shots fired at RAF Mildenhall after 'car tries to ram gate'Shortly before 4pm, a spokeswoman for Suffolk Constabulary was unable to confirm whether the matter was being treated as terrorist-related.
A Pentagon spokesman in Washington said: 'The security incident has been contained and a suspect has been apprehended.'
The lockdown ended at around 3.30pm, just under two hours after the incident began.
A statement on the base's Facebook page said: 'Lockdown has terminated on base and operations are returning to normal.
'We've concluded our combined US-UK response to this incident and we are continuing to support local authorities in the ongoing investigation.'
A member of staff at Jumppin Jacks Funhouse in Mildenhall earlier told the Press Association: 'All the American children playing here suddenly left, but we didn't hear anything or know why.'
The base has previously been identified as a potential target for terrorists.
In May 2016, Junead Khan was given a life sentence at Kingston Crown Court for planning a strike against American military personnel in Britain.
Khan, of Luton, used his job as a delivery driver to scout bases including Mildenhall and nearby RAF Lakenheath the previous year.
No other police forces are thought to be involved in the incident at this stage.
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