Attorney General Maura Healey, prompted by the recent mass shootings in Colorado and California, has warned the state’s 350 licensed gun dealers that they must obey the state’s strict gun laws and has been investigating several dealers suspected of selling illegal firearms, according to an official with knowledge of the matter.

The dealers under investigation are suspected of selling handguns or assault weapons that are banned under the state’s gun laws, which were tightened last year and have long been considered among the toughest in the nation.

In a letter Tuesday, Healey also reminded every gun dealer in the state of the obligation to follow the law, which, among other restrictions, forbids the sale of semiautomatic assault weapons and magazines that carry more than 10 rounds of ammunition.

In addition, her office said it would dispatch investigators to conduct spot checks on gun stores across Massachusetts. Dealers convicted of selling illegal guns could face up to 10 years in state prison.

Healey’s campaign reflects increasing national concern about gun violence following the recent attacks on a Planned Parenthood clinic in Colorado Springs, Colo., and at a holiday luncheon for county employees in San Bernadino, Calif.

In her letter, Healey says nearly 100,000 people nationwide have been killed with a gun since the massacre of 20 children and six adults at Sandy Hook Elementary School in Newtown, Conn., three years ago. “For me, this is a public health crisis and acting to address it is a moral imperative,’’ Healey tells the gun dealers. “There are simply too many guns that are too easy to obtain.’’

In an interview, Healey acknowledged that most Massachusetts dealers are following the law but argued it was critical to remind them of the rules and to enforce them actively.

“They are selling weapons, they are not selling shoes, they are selling lethal weapons,’’ said Healey, a Democrat elected last year. “I do think every measure should be taken to be sure that that is done lawfully and carefully, for public safety.’’

She would not say specifically how many dealers are under investigation and she has not prosecuted any since taking office in January.

Law enforcement officials welcomed Healey’s efforts. But several dealers and gun rights advocates criticized the campaign, calling it misguided.

“The first question is: Is it needed?’’ said Jim Wallace, executive director of the Gun Owners Action League of Massachusetts, a National Rifle Association affiliate. “I haven’t heard of a lot of problems with licensed retailers in the state. I have heard a lot of complaints from licensed gun dealers’’ about confusing regulations.

Don Hunt, owner of Hunter’s Trading Post in Weymouth, said he saw no reason for Healey to target licensed dealers because the dealers he knows already obey the law.

“I can’t understand what she is talking about, other than just a political maneuver to make it seem like she’s doing something,’’ Hunt said. “We have to know this is one of the highest regulated states for obtaining a firearm and, if you’re licensed dealer, we have to know the rules and regulations under which we operate.’’

But Jack McDevitt, a Northeastern University criminologist, called Healey’s efforts “a good step in the right direction.’’

McDevitt, who led a 2013 state commission on gun violence, said that while many of the licensed dealers his panel spoke to were careful about following the law, some were not.

In June, for example, the owner of Richie’s Sporting Supply in Westport was arrested and charged with selling Glock handgun models that are either banned entirely in Massachusetts or can only be sold to law enforcement officials.

“This will put some gun dealers on notice that they may get in trouble if they don’t follow the law,’’ McDevitt said. “And the law is there is to keep guns out of the hands of people who shouldn’t be able to purchase them.’’

About 60 percent of the guns used in crimes in Massachusetts come from out of state, according to federal statistics.

“All the gun dealers I know of are responsible business people, and they comply with the law, but there’s nothing wrong with a reminder of what the regulations are,’’ said William G. Brooks III, chief of police in Norwood and president of the Massachusetts Chiefs of Police Association.

Daniel F. Conley, Suffolk County district attorney, agreed. He said he was not sure if Healey’s efforts would help to curb shootings in Boston, which have increased this year, but said it couldn’t hurt to remind dealers of their legal responsibilities.

“If this causes a dealer to take a second look at a prospective buyer, I’m OK with that,’’ he said.

Mike Sheppard, the owner of North Shore Firearms in Middleton, said he was not bothered by Healey’s effort. He said his shop has already been audited several times in eight years by agents of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives.

“I think it’s just a reminder to make sure everyone is crossing their T’s and dotting their I’s,’’ he said. “If you’re doing everything right, it shouldn’t be a problem.’’

Michael Levenson can be reached at michael.levenson@globe.com.