Authorities closed commuter routes in the area around the Pentagon for a few hours Friday, snarling morning rush-hour traffic, after detaining a man acting suspiciously in Arlington National Cemetery and finding a car abandoned in bushes on the side of an area road.

No explosives or other suspicious material were found in the vehicle, a red 2011 Nissan, FBI Special Agent Brenda Heck said. A backpack the detained man was carrying held bags of what Heck called a “non-explosive unknown material” that was being investigated, she said.

At the White House, Press Secretary Jay Carney said that “there were no dangerous materials or explosives found.”

Heck, who specializes in counterterrorism, said her presence in the case was intended to represent the FBI in determining whether any federal laws were violated.

She said authorities believe that the subject of the investigation, who was detained sometime after midnight, acted alone and is in his mid-20s. She provided no further details of his identity, or what he had told authorities.

A law enforcement official, speaking on condition of not being identified, confirmed that the detained man’s name is Yonathan Melaku and he is of Ethiopian background. The official did not know Melaku’s citizenship status.

Also Friday, the FBI searched a house connected to the investigation near Alexandria, Virginia, because of what bureau field office spokesman Andrew Ames called a “public safety concern.” Ames would not say whether the house was Melaku’s residence.

“After a preliminary search of the house, the FBI determined there was no immediate concern,” Ames said. “They exited the house and were waiting to obtain a signed search warrant in order to proceed.”

Police shut down Route 27 between the cemetery and the Pentagon, as well as other roads in the area, causing major morning traffic jams. The region in northern Virginia just across the Potomac River from Washington is a major commuter thoroughfare. The roads were reopened later Friday.

The security perimeter was part of the normal response to what Heck called suspicious activity, and she said roads would be reopened as soon as possible.

“From the FBI’s perspective, it was just due diligence to protect this area,” Heck said.

No charges have been filed against the detained man, Heck said, emphasizing that the investigation was still in an early stage.

According to U.S. Park Police Sgt. David Schlosser, the detained man “wasn’t forthcoming” about his identification or what he was doing in the national cemetery after midnight.

The security response was based on how authorities handle situations involving suspicious individuals or vehicles, Schlosser said.

A Department of Homeland Security statement called the situation “a law enforcement matter at this time, with the U.S. Park Police and the Arlington County Police Department as leads and other federal agencies on the scene.”

CNN’s Carol Cratty and Eric Marrapodi contributed to this report.