A gunman shot two police officers at the main entrance to the Pentagon on Thursday night, calmly pulling a gun from his coat pocket and shooting without saying a word before he was seriously wounded in a flurry of return fire, said Chief Richard Keevill of the Pentagon Force Protection Agency.

The shooting occurred at 6:40 p.m. near the end of rush hour at the public entrance of the Defense Department headquarters, near where commuters pick up Metro trains and buses. No bystanders were hit.

Injuries to the officers, who work for the Pentagon Force Protection Agency, did not appear life-threatening, said Chris Layman, a spokesman for the agency. The suspect's injuries were critical, Keevill said. Pentagon police did not release the names of the officers or suspect. It was not clear what type of gun was used, but authorities said it was a handgun.

The officers and the suspect were taken to George Washington University Hospital, and he was in Pentagon police custody.

Police declined to speculate on a motive, and a spokesman for the National Security Council said there was not enough information to know whether it was terrorism-related. Keevill said the gunman was a U.S. citizen but declined to elaborate.

Keevill said the shooter walked up to a checkpoint near the entrance. He calmly reached into his pocket as if to show a pass and instead took out a handgun and fired it, grazing the officers.

The gunman "did not say a word" and was "very cool," Keevill said.

Dozens of officers from across the area, including the Arlington County, Va., and Pentagon police forces and some military personnel, converged on the Pentagon, directing traffic and using police dogs to search vehicles arriving at the south parking lot.

Keevill said he was "pleased on a number of levels. The officers acted quickly to neutralize the threat."