By Erik Larson |  Bloomberg

New Jersey sued a California “ghost gun” company that ships partly assembled firearms kits to buyers who can avoid background checks simply by building the untraceable weapons at home.

New Jersey Attorney General Gurbir Grewal claims in a lawsuit filed Friday that U.S. Patriot Armory sold a kit for an AR-15 assault rifle to an undercover agent after receiving a cease-and-desist letter to halt sales in New Jersey. Grewal called it the first suit brought by a state against such a company.

“With the specter of mass shootings looming over schools, places of worship, and other public spaces, the need to promote both public safety and law enforcement safety has never been more urgent,” Grewal, a Democrat, said in the complaint in state court in Newark, New Jersey.

Ghost guns, legal in most states, amplify the threat of gun violence because they lack serial numbers and can be easily assembled by terrorists, fugitives and felons who are otherwise barred from buying firearms, Grewal said. New Jersey banned ghost guns last year and secured agreements from 15 companies to halt sales there, Grewal said in a statement.

The suit seeks a court order barring Apple Valley, California-based U.S. Patriot from selling ghost-gun kits or parts in New Jersey and forcing the company to disclose on its website that such sales are illegal in the state. Residents face as many as five years in prison for buying firearm parts with the intent to build a ghost gun, and 10 years if it’s an assault rifle, Grewal said.

A message left with U.S. Patriot Armory seeking comment wasn’t immediately returned.

Legally purchased AR-15 assault rifles or similar military-style weapons have been used in some of the deadliest mass shootings, including the massacres at two mosques in New Zealand last week and shootings in the U.S. such as at Marjory Stoneman Douglas High School in Parkland, Florida, last year.

The company’s website features a variety of parts for AR-15 rifles and other popular guns. It links to U.S. Patriot’s Instagram page, where a recent post says U.S. Senator Kamala Harris, who is running for the Democratic presidential nomination, wants to “rip away” the Second Amendment.

Grewal alleges U.S. Patriot sold the kit illegally in February. He also says the company falsely told buyers that the guns were legal to purchase and failed to disclose that they were exposing themselves to criminal liability.

New Jersey Gov. Phil Murphy in November signed a bill broadening one of the nation’s toughest gun laws by banning untraceable firearms, including those manufactured on three-dimensional printers.