Police are investigating an incident at Fort Meade, Maryland, where the National Security Agency is based.
Aerial shots show two vehicles at an intersection that appear to be damaged.
The incident took place near one of the gates to the complex, far from the main buildings.
In addition to the headquarters of the NSA, Fort Meade is home to 95 units from all branches of the armed forces and offices that report to several Defense Department agencies, according to the U.S. Army, which operates the base.
About 11,000 military employees and 29,000 civilians work there, according to the Army.
Some 6,000 people also live on the base, which began operations in 1917 as a garrison for World War I draftees, the Army said.