(Adds details about recovery and number of drones)
LOS ANGELES Jan 28 (Reuters) - U.S. Customs and Border Protection has grounded its fleet of drones after a crew was forced to crash a pilotless craft off the coast of Southern California because of a mechanical problem, a spokesman said on Tuesday.
The crew operating the malfunctioning drone deliberately downed it in the Pacific Ocean, 20 miles southwest of San Diego at about 11:15 p.m. local time on Monday, the official said.
The drone and systems on board were worth $12 million, he said.
"While on patrol off the Southern California coast, the unmanned aircraft, a maritime variant of the Predator B, experienced a mechanical failure," U.S. Customs and Border Protection spokesman Michael Friel said in a statement.
"The crew determined that the UAS would be unable to return to where it originated in Sierra Vista, Ariz., and put the aircraft down in the water," Friel said.
While the cause of the drone's mechanical failure wasn't known, "an abundance of caution" prompted the agency to ground the rest of its fleet, Friel said.
Excluding the one that was lost at sea on Monday, the agency has nine drones, a Border Patrol official said.
The U.S. Coast Guard assisted by providing a buffer zone so that U.S. Customs and Border Protection authorities could safely retrieve the aircraft, said Connie Terrell, petty officer and spokeswoman for the Coast Guard. (Reporting by Alex Dobuzinskis; Editing by Cynthia Johnston and Bernadette Baum)