FBI Director Robert Mueller said today the bureau was surveilling the United States with drones.

The revelation was during an FBI oversight hearing before the Senate Judiciary Committee and comes as the bureau, along with the National Security Agency, are on the defensive about revelations that they are obtaining metadata on Americans' phone records and Americans' private data from companies like Google, Facebook, Microsoft and others.

The FBI is not alone in monitoring the U.S. with drones.

Federal agencies use them to survey U.S. borders, help fight wildfires and survey dams after hurricanes. Dozens of local law enforcement agencies nationwide deploy the unmanned crafts, too.

"Our footprint is very small. We have very few," Mueller said in response to an inquiry on unmanned aircraft by Sen. Chuck Grassley (R-Iowa).

Grassley asked: "Does the FBI own or currently use drones and for what purposes?"

"Yes, for surveillance."

Grassley continued: "Does the FBI use drones for surveillance on U.S. soil?"

"Yes, in a very, very minimal way, and seldom."

Moments later, Sen. Dianne Feinstein (D-California) said drones were a huge privacy threat to Americans. The director was unprepared to answer Feinstein's questions on what "privacy strictures" are in place to protect Americans' privacy in connection to FBI drone use.

Still, Mueller said the drone program "is very narrowly focused on particularized cases and particularized leads."

The bureau had employed drones to monitor a kidnapping scene in Alabama in February, when the FBI rescued a 5-year-old boy from a bunker, unnamed sources told CNN at the time.