WASHINGTON — A gunman coolly drew a weapon from his pocket and opened fire at a security checkpoint into the Pentagon on Thursday in a point-blank attack that wounded two police officers before the suspect was critically shot.

The two officers suffered grazing wounds and were being treated in a hospital, said Richard Keevill, chief of Pentagon police. Authorities had no motive for the shooting.

The suspect, believed to be a U.S. citizen, walked up to the checkpoint at the Pentagon’s subway entrance in an apparent attempt to get inside the massively fortified Defense Department headquarters. “He just reached in his pocket, pulled out a gun and started shooting” no more than 5 feet away, Keevill said. “He walked up very cool. He had no real emotion on his face.” The Pentagon officers returned fire with semiautomatic weapons.