FBI director Robert Mueller has admitted the agency uses drones for domestic surveillance, but claims that guidelines to restrict the technology are under development.
The information came during a questioning session of the Judiciary Committee of the US Senate in the wake of recent revelations about the data-mining methods of the National Security Agency (NSA).
US President Barack Obama said in a speech as recently as May that drone technology should not be deployed in the US and only be used for military activities abroad.
Despite the technology still being in nascent stages, Mueller admitted it could raise privacy concerns. "We already have, to a certain extent, a body of law that relates to aerial surveillance and privacy relating to helicopters and small aircraft ... which could well be adapted to the use of drones," he said.
The FBI has previously deployed the technology on several occasions, for example during monitoring exercises on the US-Mexican border, and during a six-day hostage operation in Alabama earlier this year when Jimmy Lee Dykes held a five-year-old boy hostage.
The bureau maintains it only uses drones for monitoring stationary subjects, and 'always' seeks permission of the Federal Aviation Administration (FAA).
The aerospace industry forecasts a worldwide deployment of almost 30,000 drones by 2018, with the US accounting for half.
During the session, Mueller also defended the NSA's controversial Internet surveillance programme and urged the US lawmakers not to intervene without proper consideration as it is a powerful tool allowing the intelligence services to stay one step ahead of the terrorist organisations.
"If we are to prevent terrorist attacks, we have to know and be in their communications. Having the ability to identify a person in the US, one telephone number with a telephone that the intelligence community is on in Yemen or Somalia or Pakistan ... may prevent that one attack, be that Boston or be that 9/11," he said.