Washington (CNN) -- Four Border Patrol officers who confronted armed immigrants in the Arizona desert last December were not under orders to use "less-than-lethal" force, Homeland Security Secretary Janet Napolitano said, countering critics who say an ill-advised shooting policy contributed to one of the agent's death.
But Napolitano declined to say whether two of the four agents were armed only with non-lethal "bean bag" guns, saying the incident is still being investigated.
Border Patrol Agent Brian Terry was killed December 14 when Terry and three other agents encountered a group of at least five suspected illegal immigrants in a canyon near Rio Rico, Arizona.
An FBI affidavit has raised questions about the incident, saying that two of the agents fired "less than lethal" bean bags at the armed immigrants before the immigrants returned fire.
"Our lethal force policy is the same as virtually every law enforcement department that I know of," Napolitano said. "And that is, if you are under threat of serious injury or death, you may use lethal force."
The issue arose during questioning by Sen. Charles Grassley, R-Iowa, at a Senate Judiciary Committee oversight hearing.
In the FBI affidavit, Special Agent Scott Hunter said the Border Patrol agents, using thermal binoculars, spotted at least five suspected illegal aliens near midnight in Peck Canyon. At least two of the immigrants were carrying rifles, the affidavit said.
As the aliens drew near, one of the agents identified himself as an officer and ordered the men to drop their weapons.
"When the suspected aliens did not drop their weapons, two Border Patrol agents deployed 'less than lethal' bean bags at the suspected aliens," Hunter wrote. "At this time, at least one of the suspected aliens fired at the Border Patrol agents," striking Terry, Hunter wrote.
Then two agents returned fire with a long gun and a pistol, striking one of the aliens, Hunter wrote.
Grassley said federal officials told Terry's family that two of the four agents were armed only with non-lethal bean bag guns. He asked Napolitano if that was true.
Napolitano said she did not know, but added it is not unusual for law enforcement agencies to carry a combination of lethal and non-lethal weaponry.
"The particulars of the Brian Terry operation are still under investigation and I think the facts will come out over time," she said.
Asked if the four officers were under standing orders not to use deadly force, Napolitano responded: "I have asked that question and my information is 'absolutely not.' Our lethal force policy is what I described to you."