An unidentified law enforcement official told The Washington Post the man, who was subdued and taken into custody following an altercation in the lobby of the council's headquarters, made remarks about the right-wing group's positions. He was also carrying a bag from Chick-Fil-A, the restaurant chain that became controversial when its chief executive opposed gay marriage in an interview.
James McJunkin, head of the FBI's Washington field office, would not speculate on a motive. He said agents were trying to determine if the shooting was an act of domestic terrorism or a hate crime.
"We don't know enough about him or his circumstances to determine what his connection is to this group or his mental state, or what he was doing or thinking of doing," McJunkin said. "So we're going to try to sort this all out, pull the evidence together, do all the interviews we can."
Washington Police Chief Cathy Lanier said the shooting occurred in the lobby just before 11 a.m., the Post reported. She said the man walked in and got involved in a fight with the security guard who asked him what he was doing there.
The guard and others in the lobby were able to retrieve the man's gun after getting him down on the ground, Lanier said. She said the guard was shot in the arm and was in stable condition.
"The security guard here is a hero, as far as I'm concerned," Lanier said. "He did his job. The person never made it past the front."
The council, founded in the 1980s by the Rev. James Dobson, is a conservative Christian group that opposes abortion, gay marriage and euthanasia.
The alleged gunman was in the custody of the FBI. His identity has not been released and Lanier would not speculate on his motive for going to the council's offices.
"The police are investigating this incident," Tony Perkins, the organization's president, said in a statement. "Our first concern is with our colleague who was shot today. Our concern is for him and his family."