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