An estimated 10,000 “copycat” assault weapons were sold in Massachusetts last year alone, the state attorney general’s office announced Wednesday. 

That revelation is prompting Attorney General Maura Healey to issue a notice to all gun sellers and manufacturers in the state that her office will step up enforcement of the state’s assault weapons ban, including a crackdown on such copycat sales. 

That state law mirrors a federal ban that expired in 2004, prohibiting specific name-brand weapons, as well as copies or duplicates of those weapons. 

Some manufacturers market what are known as “state compliant” versions of those same guns, with minor tweaks to various parts of the weapon, a statement from the office said. 

The state considers a firearm a copycat if the gun’s internal operating system is essentially the same as those of a specifically-banned weapon, or if the gun has key functional components that are interchangeable with those of a banned weapon.

“The gun industry has openly defied our laws here in Massachusetts for nearly two decades,” Healey said in a statement. 

“That ends today. We have a moral and legal responsibility to ensure that combat-style weapons are off our streets and out of the hands of those who would use them to kill innocent people. Increasingly, these guns are the weapon of choice for mass shooters, and we will do everything we can to prevent the kinds of tragedies here that have occurred in places like Orlando, San Bernardino, Newtown and Aurora.”

"These types of assault weapons have no place on our streets,” Boston Police Commissioner William Evans said. “We have tough gun laws in our state, and this notice will make them even tougher. I applaud AG Healey and her efforts to help make our state and all our cities safer."

The guidance will not be enforced against gun owners who bought or sold these weapons before July 20.