The legislation includes provisions that would help states keep guns out of the hands of those deemed to be a danger to themselves or others and close the so-called boyfriend loophole by blocking gun sales to those convicted of abusing unmarried intimate partners.

After mass shootings at a New York grocery store and a Texas junior school that authorities said were committed by teenagers, the legislation would allow states to provide juvenile records to the national background check system for gun purchases.

The bill stops short of raising the age limit from 18 to 21 on purchases of automatic assault weapons. The shooters in both Texas and New York were 18-year-olds who used assault rifles they bought themselves.

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Senate Majority Leader Chuck Schumer said he expected the bill to pass this week, while Senator Chris Murphy, the lead Democrat in talks to craft a legislative deal with Republicans, called it “the most significant piece of anti-gun-violence legislation Congress will have passed in 30 years”.

“This is a breakthrough,” Murphy said on the Senate floor ahead of the bill’s release. “And more importantly, it is a bipartisan breakthrough.”

The Republican leader in the Senate, Mitch McConnell, called the legislation “a commonsense package” and pledged his support.

With the 100-seat Senate split evenly between the two parties, the legislation will need support from at least 10 Republicans to pass a procedural hurdle. Fourteen Republicans, including McConnell, joined all 50 Democrats to move toward voting on the legislation.

The biggest gun lobby in the country, the National Rifle Association, said on Twitter that it opposed the legislation because it could be abused to restrict lawful gun purchases. The politically powerful group’s statement could affect how many Republicans vote on the measure.

Senator John Cornyn, the lead Republican negotiator in the bipartisan talks, held out hope the legislation would succeed.

“We know there’s no such thing as a perfect piece of legislation. We are imperfect human beings. But we have to try, and I believe this bill is a step in the right direction,” Cornyn said on the Senate floor.

The bipartisan group has been working on a deal to curb gun violence since a gunman killed 19 children and two teachers at an junior school in Uvalde, Texas, less than two weeks after 10 people were killed in a racist shooting at a supermarket in Buffalo, New York.

Lawmakers reached agreement on a provision to encourage states to adopt “red flag” laws, in which guns can be temporarily taken away from people who are deemed dangerous. It also provides funding for states that use other forms of intervention to accomplish the same outcome.

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The bill also aims to close the “boyfriend loophole” by allowing authorities to block gun purchases by those convicted of misdemeanour domestic abuse against partners to whom they are not married.

The last significant federal gun control legislation was passed in 1994, banning the manufacture for civilian use of assault rifles and large capacity ammunition clips.

But it expired a decade later and there has been no serious effort at reform since, despite rising gun violence.

Additional reporting by Agence France-Presse