Wayne LaPierre, the firebrand executive vice-president of the National Rifle Association, came under intense questioning from Democratic members of the senate judiciary committee who forced him to admit that the NRA's opposition to gun control has grown more extreme over the past 15 years.

In the course of a four-hour senate hearing on gun violence that also heard impassioned testimony from the former US congresswoman Gabrielle Giffords, LaPierre was forced to admit that the NRA no longer supported the idea of extending federal background checks on private gun sales at gun shows.

The admission revealed the increasingly extreme position adopted by the NRA, which is seen as a major roadblock in the Obama administration's hopes of passing new gun controls through Congress in the wake of the Sandy Hook school shooting last month.

LaPierre also had to endure the dramatic testimony of former Arizona congressman Gabby Giffords and her husband, Captain Mark Kelly, who sat just feet away from him. Giffords delivered her longest and most impassioned speech since she was shot in the head during the 2011 Tucson shooting, in which six people died and 13 were wounded.

After walking gingerly into the chamber, led by her husband Mark Kelly, Giffords took her seat in front of the Senate judiciary committee to deliver a prepared statement.

In front of a packed but hushed public gallery, Giffords told the committee in a halting voice: "Speaking is difficult. But I need to say something important. Violence is a big problem. Too many children are dying, too many children. We must do something. It will be hard, but the time is now - you must act. Be bold. Be courageous. Americans are counting on you."

Giffords, who has been left partially blind, paralysed in her right arm and struggling to speak and walk, was supported by her husband, who fleshed out her impassioned call for action. Kelly emphasised that he and his wife were gun owners: "We are simply two reasonable Americans who have said: enough."

Kelly, a retired astronaut, pointed out that the Tucson gunman, Jared Lee Loughner, suffered from severe mental illness and yet when he was subjected to a background check at a sporting goods store, no mention of his history cropped up. That was not surprising, Kelly said, as Arizona had failed to put on its database about 121,000 records of mental illness that would disqualify people with mental health problems from owning guns.

Kelly said that if such inadequacies and loopholes were closed, "we will prevent future gun violence. That is a fact. My wife would not have been sitting in that seat today if we had had stronger background checks."

Despite such emotional testimony from two of the most high-profile victims of mass shootings in America, the NRA's LaPierre stuck to his by now familiar script. In prepared comments, he told the senators that "law-abiding gun owners will not accept blame for the acts of violent or deranged criminals".

He also repeated his call for armed security guards to be placed in all schools as his main recommendation for preventing a repeat of the tragedy in Newtown on December 14, in which 20 young children and seven adults were killed. "It's time to throw an immediate blanket of security around our children," he said.

But Democratic members of the bipartisan senate panel turned up the heat on LaPierre. The chairman of the committee, Patrick Leahy, reminded LaPierre that in 1999 the NRA had supported the idea of mandatory background checks at gun sales. Under current laws, private sellers at gun shows do not have to subject their customers to any federal monitoring – a loophole that allows criminals and those who are mentally ill to bypass federal controls.

As a result, about 40% of guns are sold via gun shows or on the internet, entirely outside the federal system for preventing weapons falling into the wrong hands.

"Do you still, as you did in 1999, support mandatory checks in gun shows?" Leahy asked LaPierre. When LaPierre gave an evasive answer, Leahy said: "Let's not play games here. With all due respect, that was not the question I asked."

Under further probing, LaPierre admitted that the NRA today did not support the idea of extending background checks to gun shows. "We do not, as the law right now is a failure," LaPierre said.

Later, LaPierre launched into a bizarre justification of the need to carry high-powered assault weapons. He painted a scenario following a natural disaster such as a tornado, hurricane or riot in which people feel abandoned by their government. "The only way they're going to protect themselves in the cold, in the dark, when they're vulnerable, is with a firearm," LaPierre said.

Another of the Senate witnesses, the police chief in Baltimore County, Maryland, was asked what he thought of the NRA chief's apocalyptic imagining. "I find it to be scary, creepy, [and] simply not based on logic," he replied.

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