Public disclosures about U.S. government surveillance threaten the ability of police to use powerful new technologies such as drones and mobile license plate readers.

The leak of highly classified documents by National Security Agency Edward Snowden prompted tighter restrictions on key technology advances, said Georgia Bureau of Investigation Director Vernon Keenan, speaking at the International Association of Chiefs of Police conference, Reuters reported.

The disclosures, including about monitoring of U.S. phone records, threaten to erode existing authority to use high-tech equipment, Reuters said.

"The scrutiny that the NSA has come under filters down to us," Keenan said at the annual gathering that draws top law enforcement from the United States and elsewhere with workshops, product exhibits and conferences.

He said guidelines for collecting data varied widely from state to state. License plate data is retained for 48 hours to five years, for example, depending on local law, Reuters said.

For many new technologies, there is no clear legal standard to govern their use, he said.

"If we are not very careful, law enforcement is going to lose the use of technology," he said.

New technology including advanced facial recognition software, mobile license plate readers and unmanned aircraft are reshaping U.S. law enforcement, officials said.