WASHINGTON (CNN) -- FBI Director Robert Mueller acknowledged his law enforcement agency uses drone aircraft in the U.S. for surveillance in certain difficult cases.
Mueller told the Senate Judiciary Committee on Wednesday that drones are used by the FBI in a "very, very minimal way and very seldom."
The FBI director did not say how many drones the FBI has or how often they have been used.
A federal law enforcement official said the aircraft have been used for surveillance in hostage situations and when suspects have taken refuge behind barricades.
"We use it sparingly in dangerous situations where the risk to agents' lives are at stake," the official said.
The FBI acknowledged using unmanned surveillance aircraft this year to monitor the situation where a boy was held hostage in a bunker in Alabama.
Sen. Charles Grassley, R-Iowa, asked Mueller about what guidelines the FBI has for using drones that would take into account the "privacy impact on American citizens."
"We are in the initial stages of doing that," Mueller replied. "I will tell you that our footprint is very small."
Sen. Dianne Feinstein, D-California, expressed concern that there are few regulations regarding the use of drones. "I think the greatest threat to the privacy of Americans is the drone and the use of the drone and the very few regulations that are on it today and the booming industry of commercial drones."
Mueller said he would need to check on the bureau's policy on retaining images from drones and report back to the panel.
"It is very narrowly focused on particularized cases and particularized needs and particularized cases," he said. "And that is the principal privacy limitations we have."
Members of Congress and privacy advocates have pressed for regulations on the use of drones. Sen. Rand Paul, R-Kentucky, staged a filibuster in March over the possible use of drones in strikes against citizens on the streets of America. He temporarily delayed a vote on the nomination of CIA Director John Brennan.
Attorney General Eric Holder sent Paul a letter on March 4 saying in part, "the U.S. government has not carried out drone strikes in the United States and has no intention of doing so."
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