The US Department of Justice is facing calls for new rules on drone surveillance after it was revealed the FBI has been deploying unmanned aircraft since 2006.
A report by a departmental inspector general watchdog said the FBI has spent $US3 million on drone deployment.
The BBC reports the audit was the first time the full extent of drone use in US law enforcement has been acknowledged.
It reveals that four Justice Department units, including the FBI, spent $US3.7 million acquiring and testing drones between 2004 and May this year. None of the drones were armed.
But the inspector general said the FBI risked violating privacy rights and urged new protocols to restrict improper surveillance.