The Federal Bureau of Investigation (FBI) has admitted that it used aerial surveillance drones over the US soil to aid investigations.
FBI director, Robert Mueller said that the agency used the drones 'seldom' and in a very 'minimal way', the Guardian reports.
The potential for increased use of aerial surveillance drones over US or over nations with US citizens has sparked debates about privacy safeguards.
Drones are known for use by border control officials, some local law enforcement authorities and Department of Homeland Security in criminal cases.
Dianne Feinstein, who also chairs the Senate intelligence committee, said that the issue of drones worried her far more than telephone and Internet surveillance by the NSA.
According to the report, Mueller said that the FBI is in 'initial stages' of developing privacy guidelines to balance security threats and civic liberty concerns.
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Congress senators have expressed concern over the use of drones by the agency.
Democrat of Colorado, Mark Udall said that despite the fact that drones are used to perform law enforcement duties, the American citizens expect the FBI to first protect their constitutional rights.
Another senator Chuck Grassley expressed concern and said that FBI was asked last year whether it was using drones but they never gave answers.
Mueller defending the NSA 'snooping programme' has urged the Congress to be careful about making changes or restricting the surveillance programme and said that to prevent terrorist attacks the agencies must know and track the communications, the report added.