President Barack Obama Wednesday demanded an assault weapons ban and universal background checks for gun buyers, stoking a generational clash with the firearms lobby after the Newtown school massacre.

"We can't put this off any longer. I will put everything I've got into this," Obama said, laying out the most sweeping gun control legislation in decades and daring Congress not to defy public outrage and block his plans.

Obama signed 23 executive actions, using his presidential power in a swift effort to check a rash of gun violence including the killings of 20 kids at Sandy Hook Elementary School last month and other recent mass shootings.

And he challenged Congress to enshrine enduring reforms into law, including renewing and bolstering a ban on assault weapons, and closing loopholes that permit 40 percent of gun sales to take place without background checks.

"This will be difficult," Obama warned, unveiling measures drawn up by a task force led by Vice President Joe Biden at a White House event attended by gun crime victims, including the parents of a girl who perished in Newtown.

"There will be pundits and politicians and special interest lobbyists publicly warning of a tyrannical all-out assault on liberty," Obama said.

"Behind the scenes, they'll do everything they can to block any commonsense reform and make sure nothing changes whatsoever," Obama said, underlining he did not oppose the right to bear arms laid down in the US Constitution.

The National Rifle Association, the top gun lobby group, warned that only law abiding gun owners would be affected, and "our children will remain vulnerable to the inevitability of more tragedy."

Immediate reaction from pro-gun politicians to Obama's plans to curb 11,000 annual firearms homicides in America also hinted at the unpromising political terrain the president's plans face.

Senate Democratic majority leader Harry Reid welcomed the "thoughtful" proposals but gave no commitment to act on specific measures.

While background checks may attract support, a ban on assault weapons could force many Democrats from largely conservative states to unwelcome tough votes in the run-up to the 2014 mid-term election.

Several prominent Republicans rejected Obama's plans out of hand, accusing him of attacking the right to bear arms.

"Guns require a finger to pull the trigger," Texas Republican Governor Rick Perry said.

"There is evil prowling in the world... let us all return to our places of worship and pray for help."

Republican Senator Marco Rubio, a potential 2016 presidential hopeful, added: "guns are not the problem; criminals with evil in their hearts and mentally ill people prone to violence are."

Obama appeared with four children, representing hundreds who wrote to him after the 20 children and six adults were killed when a gunman blazing an assault rifle went on the rampage in Connecticut last month.

"This is our first task as a society, keeping our children safe. This is how we will be judged and their voices should compel us to change."

Obama's executive actions, which do not need congressional approval, would require government agencies to make relevant information available for background checks to prevent "dangerous" people getting guns.

Currently, licensed gun sellers are required to run background checks on customers, but private sales of firearms benefit from a loophole.

Obama ordered a new national campaign on safe and responsible gun ownership, a review of standards for gun safes in the home, and new training for schools on how to respond to an invasion by armed assailants.

The president required the Centers for Disease Control and Prevention to research the causes and prevention of gun violence -- after some lawmakers tied the agency's hands in a bid to thwart new gun control measures.

The president urged Congress to renew a ban on assault weapons that expired in 2004 and to limit ammunition magazines to 10 rounds, in a bid to check the damage a shooter could do once engaged in a mass shooting.

The White House complained Wednesday that an NRA attack ad accusing Obama of hypocrisy because his daughters get armed Secret Service protection and other school children do not was "repugnant and cowardly."

Obama's package also seeks to crack down on guns trafficking, calling on lawmakers to equip law enforcement agencies with new powers to prosecute gun criminals.

He nominated acting director Todd Jones as the new head of the Bureau of Alcohol, Tobacco and Firearms, the top government regulatory body for firearms.

The agency has been without a director for six years after Republicans refused to allow Senate confirmation after successive nominees fell prey to heavy opposition from gun rights groups.