California law enforcement agents have seized 1,200 firearms from people who cannot legally own them because of mental illness or restraining orders.

However, Attorney General Kamala Harris said Thursday that more than 34,000 handguns and nearly 1,600 assault weapons are still believed to be held statewide by people who should not have them.

Most people bought the weapons legally but were later prohibited from owning guns.

But 12 people were arrested on suspicion of illegally owning assault weapons or grenades during a six-week sweep by the state Department of Justice in April and May.

Harris said 90 percent of the people who had guns seized were barred from owning weapons because of mental illness and 10 percent because of restraining orders or convictions usually related to domestic violence.

"They were known to be a danger to themselves or society," Harris said. "We obviously have put a dent in that, but there is a lot more work to do."

She used a news conference at the California Highway Patrol's Sacramento headquarters to promote SB819, a bill that would expand the use of a $25 registration fee collected by gun dealers to pay for the department's Armed and Prohibited Persons System.

The system was created 10 years ago to cross-reference five databases to find people who legally bought guns and registered assault weapons but are now barred from owning the weapons.

It has found nearly 18,000 people who shouldn't have weapons. However, Harris said local law enforcement and state agents don't have the time or personnel to track down their addresses and conduct the high-security operations needed to safely seize the guns from people who are presumed to be dangerous. Many of them own more than one weapon.

The last time California conducted a similar sweep was in 2007, when a third as many weapons were seized.

The bill being carried by Sen. Mark Leno, D-San Francisco, would let Harris seek to use nearly $1 million from a $5.5 million surplus in the registration fee account to train local police and hire five more state agents to aid the 20 already assigned to the firearms program.

"Resources are needed to do this type of work," Leno said against a backdrop of seized weapons. "How many lives are going to be saved?"

His bill cleared the Senate and is awaiting a hearing in the Assembly Public Safety Committee on Tuesday.