Describing it as “urban terrorism,” California Atty. Gen. Jerry Brown joined with Riverside County officials Thursday in asking the public to help find those who tried at least three times to kill officers assigned to a Hemet-based gang task force.

“It is incredible and even unprecedented for police officers here to be subject to terrorist attack,” Brown said at a Riverside news conference. “We have seen it south of the border, but not here yet.”

The attacks have involved booby traps aimed at either the headquarters of the Hemet-San Jacinto Gang Task Force or officers assigned to the unit, officials said.

Last December a utility line was redirected to flood the offices with gas so any spark would cause an explosion. In February, a modified handgun was hidden by the gate to the office and rigged to fire. When a gang officer opened the gate, the weapon went off, narrowly missing him. And two weeks ago, police said, a “dangerous” device was found near the unmarked car of a task force member.

Officials have put up a $200,000 reward for information leading to the arrest and conviction of those responsible. The FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives is assisting in the investigation.

“Unfortunately, somebody out there is trying to kill our police officers,” said Hemet Police Chief Richard Dana. “The only reason they haven’t killed an officer yet is because [officers] have been observant enough to see the devices, but we can’t expect their luck to hold up.”

He said the department is toughening security at its offices, including erecting fences and barricades. Dana said his officers had spotted people watching his headquarters.

The gang task force was formed in 2006 and comprises local, state and federal law enforcement agencies.

So far there are no suspects, but on Wednesday authorities said they led raids on the Vagos outlaw motorcycle gang, which has a large presence in Hemet. Thirty people were arrested on charges that included possession of drugs and weapons.

“They aren’t your typical street gang hanging out on a corner slinging rock cocaine,” said Riverside County Dist. Atty. Rod Pacheco. “It is a well-established pattern of the Vagos to infiltrate police departments. They do a lot of surveillance.”

david.kelly@latimes.com