CNN) -- A man coolly walked up to the Pentagon's screening area Thursday evening and opened fire, slightly wounding two Pentagon police officers before they returned fire, critically wounding him, officials said.
The incident happened at 6:40 p.m., when the man -- with "no real emotion in his face" -- approached the officers outside the Pentagon Metro station, said Pentagon Police Chief Richard S. Keevill.
"As the officers started to ask him for his pass to get into the Pentagon, he drew a weapon from his pocket and started shooting" from a few feet away, Keevill told reporters.
The two Pentagon Force Protection Agency officers returned fire with their semi-automatic weapons and the suspect, thought to be a U.S. citizen, was critically wounded, Keevill said. "He did not say a word," Keevill added.
Pentagon entrances were locked briefly, but all were reopened with the exception of the Pentagon Metro entrance, the Pentagon said in a statement.
The Pentagon Force Protection Agency is the Pentagon's police department.
Lisa McDonald, a spokeswoman for George Washington Hospital, told CNN three people were being treated there -- both officers and the suspect.
The U.S. Secret Service and the FBI were both involved in the investigation, Keevill said.
