Afghan troops had already been told not to bring their guns in.
"Something has come to light," Sgt. Maj. Brandon Hall told the troops. It was a highly unusual order, and some in the audience said they had never seen that happen before.
Asked about the order, Hall said all he knew was that "I was told to get the weapons out."
A U.S. defense official said the request was not a reaction to an immediate threat. Speaking on condition of anonymity to describe security procedures, the official said the base commander made the decision that no one would be allowed to bring in weapons.
The official said the decision was made out of respect for troops from other countries, such as the Afghans, who are never allowed to bring guns into an event. It was not a request from Panetta or his security team, the official said.