Plans to bar firearms sales to terror suspects are unconstitutional, one of the most powerful politicians in the US has said.
House of Representatives Speaker Paul Ryan signalled there will not be a vote on proposed Democratic gun curbs, as the election-year clash over firearms showed no sign of resolution.
The House Speaker is second in the US presidential line of succession after the vice president, and met Democrats who are campaigning over the issue, who said they told him: "We're not going away."
Mr Ryan, who represents Wisconsin, said in an interview that Democrats' plans to broaden required background checks for gun buyers and to bar firearm sales to terror suspects were unconstitutional.
And although he did not directly say he would block votes on the proposals, he stressed Republicans had no intention of rewarding Democrats for their lengthy House floor sit-in two weeks ago to demand gun-control votes.
"Win elections and get the majority, then you can set the agenda," he said.
Mr Ryan met two leaders of the sit-in, representatives John Lewis of Georgia and John Larson of Connecticut, in a private session the Democrats described as respectful.
"We wanted action, and we wanted action now," Mr Lewis, the civil rights hero, said of their message to Mr Ryan.
"We're not going away," Mr Larson said. "And we're determined in that effort."
Mr Ryan's spokeswoman AshLee Strong said the two parties "have different views on how to achieve a shared goal of preventing gun deaths" - especially over how to protect gun owners' rights.
The House convened peacefully on Tuesday for its first session since Democrats seized control of the chamber last month with a sit-in that lasted almost 26 hours.
The Republicans had planned to approve party legislation this week that would let federal authorities block gun sales to suspected terrorists, but only if they could prove in court within three days that the suspect was planning to engage in terrorism.
That bill, which resembles National Rifle Association legislation that the Senate rejected last month, is considered ineffective by Democrats because they say the mechanism it sets would prove too complicated.
Even so, it reflects the pressure for action the June 12 mass shooting in Orlando, Florida, has placed on Republican leaders, who since the 2012 killing of schoolchildren in Newtown, Connecticut, have not brought broad gun restrictions to the House floor.
Forty-nine victims were killed in Orlando, the worst mass-shooting in modern American history. It was conducted by Omar Mateen, a gunman who pledged support for leaders of the Islamic State extremist group, according to transcripts of his conversations with authorities.