Authorities today closed several major highways around the Pentagon while investigating a nearby vehicle, after taking a man into custody.
Police said they discovered the man in nearby Arlington National Cemetery during the predawn hours and traced him to a car abandoned near a Pentagon parking lot.
US Park Police Sergeant David Schlosser could not confirm earlier reports that authorities had discovered a suspicious package inside the vehicle and were searching for as many as three others who had fled the scene on foot.
"There is no suspicious package I'm aware of," he told reporters.
But he said the area was being swept for explosive devices as a precaution.
The incident was being investigated by several agencies including the FBI and Pentagon police. A US official described it as "a law enforcement matter."
The Pentagon has been the scene of a number of security incidents since the September 11 attacks in 2001, including an exchange of gunfire outside the building between a man and security guards in March 2010.
Last December, an unattended blinking package prompted authorities to shut the Pentagon's subway station for 90 minutes during rush hour. It turned out to be a Christmas ornament.