US President Barack Obama has unveiled the most sweeping gun control proposals in two decades, setting up a showdown with firearms rights advocates.
He called for a ban on assault weapons and high-capacity magazines and wider background checks on gun buyers.
The Democratic president also signed 23 executive actions, which do not require congressional approval.
A month after the school massacre in Connecticut, he said gun-control reforms could wait no longer.
Mr Obama unveiled the proposals at the White House on Wednesday, flanked by children who wrote him letters after December's Newtown shooting, which left 20 children and six teachers dead.
Mr Obama said: "If there is even one thing we can do to reduce this violence, if there is even one life that can be saved, then we've got an obligation to try."
The top US gun lobbying group, the powerful National Rifle Association (NRA), said the proposals were "not a solution to the crisis we face as a nation".
"Only honest, law-abiding gun owners will be affected and our children will remain vulnerable to the inevitability of more tragedy," the group said in a statement.
The president urged Congress:
- to reintroduce an expired ban on new purchases of "military-style" assault weapons, such as those used in several recent mass shootings
- limit ammunition magazines to 10 rounds and pass a ban on possession and sale of armour-piercing bullets
- introduce background checks on all gun sales; currently private purchases and some transactions at gun shows are exempt
- introduce harsher penalties for gun-traffickers, especially unlicensed dealers who buy arms for criminals
- finally approve the appointment of the head of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives
Mr Obama also signed 23 unilateral orders, including an end to a ban on gun-violence research by a prominent federal agency, and a measure promoting responsible gun ownership.
But he acknowledged his legislative push would encounter stiff opposition in Congress.
"This will be difficult," he said.
"There will be pundits and politicians and special interest lobbyists publicly warning of a tyrannical, all-out assault on liberty -- not because that's true, but because they want to gin up fear or higher ratings or revenue for themselves.
"And behind the scenes, they'll do everything they can to block any common-sense reform and make sure nothing changes whatsoever."
Republican National Committee Chairman Reince Priebus dismissed Obama's measures.
"He paid lip service to our fundamental constitutional rights," Mr Priebus said of the president, "but took actions that disregard the second amendment and the legislative process."
'Repugnant and cowardly'
The US has one of the highest rates of civilian gun ownership in the world. The second amendment of the US constitution states that "the right of the people to keep and bear arms shall not be infringed".
Although the meaning of the full clause is still debated, many gun-rights advocates read it absolutely and oppose the idea of any curbs on access to weapons.
The White House proposals follow meetings between a task force led by Vice-President Joe Biden and groups from across the political spectrum.
Mr Biden met gun control and firearms rights advocates, entertainment and video game industry figures, parents of shooting victims and law enforcement officials.
The task force also consulted the NRA, which says it has signed up more than 100,000 members since the Newtown massacre.
Earlier, the NRA released a web advert attacking Mr Obama as "an elitist hypocrite" for allowing Secret Service agents to protect his daughters, while not committing to back armed guards in all US schools.
The White House said the ad was "repugnant and cowardly".
On Wednesday, Mr Obama also proposed freeing up law enforcement funds for schools to hire 1,000 new armed police, school psychologists, social workers or other staff trained to prevent violence.