At least 12 states, including New York, Connecticut and Washington, have moved to increase fees and taxes on guns and ammunition since the Sandy Hook school shooting in 2012, according to a study by Southern Illinois University.

Though higher fees might discourage some people from buying firearms, gun control advocates and researchers said they were not certain that higher fees alone would reduce violence.

“Most crime guns in the Northeast are thought to come from the ‘iron pipeline’ from the South, and then they’re sold on the street,” said Daniel L. Feldman, a professor at John Jay College of Criminal Justice, referring to guns that are bought in states with looser restrictions and then sold illegally in states with tighter ones.

But gun control groups do support the idea of raising the cost of owning a firearm to pay for programs that would make it harder to use guns to commit crime.

“We think it’s a smart way to legislate,” said Jonas Oransky, the legal director at Everytown for Gun Safety, a gun control group founded by Michael R. Bloomberg, the former New York City mayor.

“We support strong data-driven intervention programs,’’ he added, “and think that it makes sense to fund them by raising revenue from gun purchasers.”