WASHINGTON - An American drone that is part of a fleet that patrols the border with Mexico has crashed off the coast of Southern California.

Customs and Border Protection says the drone was being flown on a border security mission when a mechanical problem developed about 20 miles southwest of San Diego late Monday. Spokesman Mike Friel says the crew operating the drone decided to crash it in the ocean.

The $12 million surveillance drone was one of 10 that the Department of Homeland Security uses to patrol the border. It was just one of two Predator B drones equipped with radar specifically designed to be used over the ocean.

Friel said the cause of the mechanical failure is unknown.