US President Barack Obama has called for speedy action on gun control measures and vowed to use "whatever weight this office holds" to make them a reality.
He was speaking as he announced a $500 million package that sets up a fight with the US Congress over bans on military-style assault weapons and high-capacity ammunition magazines.
The move comes just a month after a shooting in Connecticut killed 20 school children.
Mr Obama also signed 23 executive actions, which require no congressional approval, requiring federal agencies to make more data available for background checks, appointing a full-time director of the Bureau of Alcohol, Tobacco, Firearms and Explosives, and directing the Centers for Disease Control to research gun violence.
However Mr Obama acknowledged the most effective actions must be taken by politicians.
He said: "To make a real and lasting difference, Congress must act. And Congress must act soon."
Mr Obama was flanked by children who wrote letters to him about gun violence in the weeks following the Connecticut shooting.
Families of the children killed in the Newtown shooting, as well as survivors, were also in the audience.
The announcement promises to set up a bitter fight with the powerful pro-gun lobby, the National Rifle Association, which has long warned supporters that Mr Obama wanted to take away their guns.
In a statement released following Mr Obama's announcement the NRA largely dismissed his proposals, saying they amounted to an attack on firearms and would affect only law-abiding gun owners.
"We look forward to working with Congress on a bi-partisan basis to find real solutions to protecting America's most valuable asset - our children," the statement said.
"Attacking firearms and ignoring children is 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 NRA said.
The US has the highest rate of gun ownership of any country in the world, and pro-gun groups see any move on gun restrictions as an offence against the right guaranteed by the Second Amendment of the US Constitution.
Critics counter that the country's founding fathers never could have foreseen assault weapons more than two centuries ago.
"This is the land of the free and the home of the brave and always will be," Mr Obama said, acknowledging the right to bear arms.
"But we've also long realised ... that with rights come responsibilities."
Emotions have been high since the Connecticut shooting, which Mr Obama has called the worst day of his presidency.
He largely ignored the issue of gun violence during his first term, but appears willing to stake his second term on it now.
He will have to contend with looming fiscal issues that have threatened to push whatever he proposes aside, at least for a while.
Gun control advocates also worry that opposition from the powerful NRA and its allies in Congress will be too great to overcome.
The NRA yesterday released an online video that called Mr Obama an "elitist hypocrite" for having armed secret service agents protect his daughters at school, while not committing to installing armed guards in all schools.
The NRA insists that the best way to prevent more mass shootings is to give more "good guys" guns.
The White House called the NRA video "repugnant and cowardly".
Meanwhile, New York has become the first US state to pass new laws aimed at curbing gun violence.
The law puts further limits on the purchase of assault rifles and the size of ammunition magazines.
It also makes it harder for someone with mental health problems to acquire a weapon.
