MONTERREY, Mexico (Reuters) - Three Mexican minors detained in California on suspicion of smuggling drugs stole a U.S. Border Patrol car while still wearing handcuffs and drove it back across the border to Mexico.

Police in the Mexican border city of Mexicali said on Tuesday the three boys had been driving a pick-up truck on a remote Californian highway when a Border Patrol agent stopped them.

Suspicious they were carrying marijuana, he handcuffed them and put them in his patrol car while he searched their truck.

"As the agent was doing his search, he left the vehicle running and the keys in the ignition, so one of the lads, still wearing handcuffs, grabbed the steering wheel and they headed back to Mexico," a police spokesman said.

The Border Patrol, which plays cat and mouse around the clock with illegal Mexican migrants and drug traffickers, confirmed the vehicle was stolen in southern California on Sunday and driven over the border near Mexicali.

Mexican police used a helicopter to locate the patrol vehicle in a remote agricultural area near the border.