Some Maryland officials think the state’s strict handgun-purchasing law won’t work as effectively unless other states adopt similar rules. (Neil Hall/Reuters)

U.S. Rep. Chris Van Hollen and Maryland Attorney General Brian E. Frosh on Wednesday called for other states to join Maryland in requiring licenses to purchase handguns, saying the rule works best to stem gun violence when it applies across jurisdictions.

During a news conference with other gun-control advocates at a Baltimore County courthouse, the officials said that firearms tend to flow from states that lack permit-to-purchase laws to those that have them, with guns often landing in the hands of criminals.

Ten states and the District of Columbia have licensing requirements for handguns, but the Maryland border states of Pennsylvania, West Virginia and Virginia do not.

Van Hollen (D-Md.), a candidate for the Democratic nomination for the Senate, has introduced legislation that would provide financial incentives for states to adopt purchasing laws similar to the one that Maryland enacted in 2013, which requires fingerprinting and licensing.

Frosh (D) supported the legislative effort on Wednesday by issuing a letter to the attorneys general of every state citing what he described as “clear evidence” that such gun-control laws have decreased firearm-related deaths where they are enacted.

He pointed to studies from the Johns Hopkins Center for Gun Policy and Research, which found that gun-related homicides dropped by 40 percent over 10 years in Connecticut after the state adopted a permit-to­-purchase law in 1995, whereas Missouri’s numbers increased by 25 percent after the state repealed a similar statute in 2007.

“These peer-reviewed analytical studies lead to a clear narrative about the impact of permit-to-purchase laws,” Frosh said in his letter. “Simply put, they save lives.”

Wednesday’s event, which featured federal, state and county officials, took place on the eve of the second anniversary of the effective date for Maryland’s 2013 licensing law. Frosh helped shepherd the legislation through the General Assembly as a state senator that year.

Jenifer Pauliukonis, legislative chair of Marylanders to Prevent Gun Violence, said at the news conference that Maryland’s statute should serve as a model for states across the nation. “The country deserves more than a couple of states having common-sense gun laws,” she said.

Pauliukonis scolded elected officials across the country who have resisted gun-control efforts despite an alarming rise in mass shootings and other firearm­-related deaths.

“I’ve watched as so many cowardly leaders in Congress have done nothing,” she said. “They have done nothing when faced with nauseating statistics of gun deaths, and they did nothing when faced with gun-violence survivors and parents whose children have been destroyed by these bullets.”

Van Hollen, who described gun violence as a “disease” and an “epidemic,” said that too many national leaders are “worried about the politics of the gun lobby.”

Gun-control opponents such as the National Rifle Association have argued that permit-to-­purchase laws restrict the constitutional rights of peaceable Americans to bear arms, while doing nothing to prevent criminals from obtaining firearms using illicit means such as theft, straw purchasers or the black market.

Daniel Webster, a public-health professor at Johns Hopkins University and the director of the Center for Gun Policy and Research, acknowledged Wednesday that most guns used in violent crimes have come from the streets. But he said that permit-to-purchase laws can help “reduce that flow of guns that get diverted into the underground market.”

Webster said the impact of Maryland’s law is hard to quantify now, because only one year of crime data is available, but he added that he expects evidence of improvement to emerge “in the next year or two.”