By Laila Kearney

SAN FRANCISCO (Reuters) - Two Mexican nationals were indicted on Thursday on charges of running an outlaw weapons-supply shop in northern California that assembled and sold unmarked, illegal firearms and accessories, including machine-guns and silencers.

A federal grand jury in Sacramento indicted brothers Luis Cortez-Garcia, 44, and Emiliano Cortez-Garcia, 37, on one count each of unlawful manufacturing and sales of firearms, conspiracy to unlawfully manufacture and sell firearms and multiple counts related to making and selling illegal assault rifles, U.S. Attorney Benjamin Wagner said in a statement.

"The conduct alleged in this case involves the systematic evasion of federal firearms laws, for profit, in a manner that created a real threat to public safety," Wagner said.

Additionally, both brothers were charged with being illegal immigrants in possession of firearms.

The men are accused of belonging to a network of criminal arms manufacturers and dealers with operations across central and northern California.

They are suspected of running outlaw supply shops in Sacramento and Fresno where they would assemble firearms for customers who bought gun components from the brothers or from other members of their network, Wagner said.

The brothers are also accused of illegally selling fully functional unmarked firearms that were purchased in cash by customers without required background checks, waiting periods or proper paperwork, officials said.

The Cortez-Garcias were arrested during raids last fall by federal and local law enforcement officers on 11 locations where 345 unlicensed guns were seized, officials said.

Danny Brace, a private attorney representing Luis Cortez-Garcia, said his client and his brother deny ever fully assembling or selling a firearm. He said the men were lawfully assisting customers in assembling rifle parts.

Federal law allows a person to manufacture a firearm without a serial number for personal use, as long as it is not sold or transferred to another person.

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"They were open for business," Brace told Reuters. "They weren't trying to hide anything."

The brothers face five to 10 years in federal prison for each count against them if convicted, but they would likely serve that time concurrently, Justice Department spokeswoman Lauren Horwood said.

They were being held without bail at the Sacramento County Jail, awaiting an arraignment date, Horwood said.

(Editing by Steve Gorman and Ken Wills)