LONDON — An air base in England that is used by the United States Air Force was put on lockdown on Monday after American military personnel responded with gunfire to an intruder who tried to force his way through a checkpoint.

A suspect, who has not been publicly identified, had cuts and bruises and was taken into custody after the episode — the Suffolk Police called it a “significant incident” — broke out around 1:40 p.m. at the Mildenhall air base, about 75 miles northeast of London.

“An individual came through the gate and failed to yield to commands to stop,” said Brian Boisvert, a spokesman for the United States military at the base, adding that safety protocols were followed and shots were fired as a last resort.

The Suffolk Police said that there were no other reports of injuries, that officers were on the scene, and that members of the public should avoid the area.