WASHINGTON (AP) — The FBI says armored car robberies have spiked in Washington over the last year, and as investigators look for possible links between the heists they also worry about the risk of violence that accompanies them.

The 12 robberies or attempts since March 2010 far outpace the roughly two to four the city has experienced in previous years, said Ronald Hosko, special agent in charge with the FBI’s Washington field office.

“That has our attention,” Hosko told The Associated Press an in interview Thursday. “That is, relatively speaking, a fairly significant jump.”

The FBI is exploring links between the cases, including what officials say was a foiled attempt that resulted in the arrests this month of three men. Arrests have been made in four of the cases, the FBI said.

Hosko said he was unaware of other parts of the country that have experienced similar increases in armored car robberies, but that last year’s total in Washington accounted for a relatively large percentage of the roughly 60 to 70 reported in the country in a typical year.

No one has been killed in any of the robberies, though gunshots have been fired in some of the incidents. Hosko won’t say how much money has been stolen.

He said the FBI was especially concerned because of the inherent risk of violence.

“You’re potentially coming to a gunfight every time because you’re going to encounter armed people,” Hosko said. “They’re guarding the assets of the armored car company, and the robberies are going to be very much dependent on the reaction of the people with the money and the guns.”

This month, officials say, three men were charged after they were spotted trailing a Brinks Inc. armored truck for several blocks. Officials seized an AK-47 assault rifle and two handguns.

A federal grand jury has indicted the three on bank robbery charges.

(Copyright 2011 by The Associated Press. All Rights Reserved.)