A recent US Supreme Court decision is hurting the ability of federal law enforcement agencies to monitor criminal suspects with global positioning satellites (GPS), according to FBI Director Robert Mueller.

"I can't speak to the numbers, but a substantial number of trackers we have had to turn off," Mueller said Wednesday before a House of Representatives committee.

An FBI official recently said at a law school conference in San Francisco that the FBI operated about 3,000 GPS devices.

In late January, a Supreme Court ruling limited the authority of police to use satellites for geolocation.

The court said police must obtain warrants before monitoring criminal suspects with GPS. Otherwise, police would infringe upon their constitutional rights of privacy.

Mueller said the ruling "is going to have an impact on the work that we do."

GPS "often saves us from physical surveillance," Mueller said. "Putting a physical surveillance team out with six, eight, 12 persons, is tremendously time-intensive."

In some cases, the FBI has lacked enough evidence to obtain warrants against terrorism suspects because of the time commitment required to gather incriminating evidence, Mueller said.

"And we are stuck in the position of surveying that person for a substantial period of time," Mueller said. GPS "trackers enabled us to utilize resources elsewhere."

The unanimous January 23 Supreme Court decision said GPS for tracking the movement of vehicles was an "intrusion."

The ruling resulted from a government appeal when an accused drug dealer's conviction was overturned by a lower court.

Some evidence used to convict the man was gathered with a GPS device after the warrant that authorized the satellite monitoring of his movements had expired.

As a result, the evidence could not be used to convict the defendant, the courts ruled.

Mueller said although wider use of GPS is useful to the FBI, "We will comply with the ruling of the Supreme Court."