The White House will keep pushing for tough new gun ownership laws despite lack of support in Congress, Vice President Joe Biden said Thursday, urging politicians to show "courage" for the sake of shooting massacre victims.

"I'm not going to rest and nor is the president until we do all of these things," Biden told a press conference in New York, where he joined Mayor Michael Bloomberg and bereaved parents from Newtown, where 20 elementary school children were shot dead in December.

"For all those who say we couldn't or shouldn't ban high capacity magazines, I ask them just one question: think about Newtown," Biden said in a brief, but emotional speech in which he referred to the "beautiful little babies" killed in the school.

Senate Democrats have conceded that their proposed ban on assault rifles, like the gun used by a deranged intruder in the Newtown slaughter, has no way of passing in Congress.

Other measures under consideration -- and that may have a better chance of being enacted -- include requiring background checks for all gun sales.

Turning to face the parents of the school teacher who was killed when she tried to confront the Newtown shooter, Biden said: "It's time for the political establishment to show the courage your daughter showed."

Bloomberg, a billionaire who has focused heavily on reducing crime in New York and on a broader anti-gun campaign across the United States, also hammered Congress.

"The only question is whether Congress will have the courage to do the right thing," he said, highlighting the huge, barely reported death toll from gun violence around the country.

"It has been 97 days since Newtown. In that time, we estimate that more than 3,000 Americans have been murdered.

"If Congress does nothing, another 12,000 people will be murdered with guns this year alone."

Despite the divide in political circles, polls show Americans overwhelmingly support universal background checks on gun purchasers, among other new regulations.

"We remain optimistic Congress will take action... because the American people could not be more clear about where they stand," Bloomberg said.

Gun control is one of the most politicized issues in a country rich in gun lore and where the Constitution is interpreted as guaranteeing the right of citizens to bear arms.

Opponents to any new gun laws, including the politically powerful National Rifle Association, argue that legal restrictions are the thin end of a wedge into constitutional rights and that criminals can in any case buy weapons illegally when needed.

However, Biden said Americans back "common sense" measures like background checks and alerts to the authorities when someone tries to amass weaponry.

"Not one (new rule) infringes on anybody's Second Amendment constitutional rights," he said.

One of the weapons used in Newtown, the popular military-style Bushmaster .223 rifle, is "a weapon of war," Biden said. "That weapon of war has no place on American streets."

The vice president also asked whether the shooter would have been capable of spraying so many bullets had he been forced to use smaller ammunition clips -- as the White House wants -- rather than the monster 30-round clips that allowed him to keep firing for longer.

Neil Heslin, whose young son was killed in Newtown, had difficulty keeping his composure as he addressed the press conference, saying: "Quite honestly, I'm really ashamed to see that Congress doesn't have the guts to stand up."