Largest gun lobby group breaks silence to say it is 'heartbroken' by Newtown shootings and plans press conference for Friday

The National Rifle Association finally broke its silence on Tuesday, offering to make "meaningful contributions" to ensure there is no repeat of the Newtown massacre.

The NRA has been heavily criticised for lying low since Friday's shooting spree at Sandy Hook elementary school in Connecticut that left 20 children, seven adults and the gunman, Adam Lanza, dead.

The normal pattern for the NRA is to say nothing in the immediate aftermath of such incidents and to emerge later, when memories begin to fade, to lobby hard against gun controls.

On Tuesday, the NRA stuck to a short statement saying it would not comment until the facts had been thoroughly investigated.

NRA spokesman Andrew Arulanandam, in a statement issued Tuesday, said the organisation "is made up of four million moms and dads, sons and daughters – and we were shocked, saddened and heartbroken by the news of the horrific and senseless murders in Newtown".

It added: "Out of respect for the families, and as a matter of common decency, we have given time for mourning, prayer and a full investigation of the facts before commenting."

In an astonishing about-turn from the NRA's normally intransigent position, it added: "The NRA is prepared to offer meaningful contributions to help make sure this never happens again."

Although the NRA may revert to outright opposition to the changes Barack Obama has promised to back – a ban on automatic weapons, and possibly closing loopholes that allow lax checks at guns shows and reducing the size of bullet clips – even making this conciliatory comment marks a rare change in its posture.

It is planning to hold what it described as a "major" press conference in Washington on Friday, a week after the massacre.

The NRA's statement came as Obama hardened up his commitment to imposing restrictions on gun ownership on Tuesday, with the White House promising to support a bill to ban assault weapons of the type used in Newtown.

White House spokesman Jay Carney said Obama supported reinstating the ban, which was first introduced in 1994 but was allowed to lapse in 2004 by the Bush administration.

Carney said Obama will support a bill that the Democratic senator Dianne Feinstein said she will introduce in January to curb the sale of automatic- and semi-automatic weapons. Feinstein was responsible for the original 1994 bill.

Carney went further, saying that Obama was also considering support for the closure of a loophole that allows easy sale at gun shows. Buyers are not subjected to the same background checks and demands for various forms of ID at these shows that they would if buying from a licensed gun store.

In another measure, Carney also signalled support for taking action to restrict ammunition clips, reducing the number of bullets to single figures, making mass killings more difficult. Obama is "interested in looking at" this, Carney said.

"He is actively supportive of, for example, Senator Feinstein's stated intent to revive a piece of legislation that would reinstate the assault weapons ban," Carney said.

"He supports and would support legislation that addresses the problem of the so-called gun show loophole, and there are other elements of gun legislation that he could support … high capacity ammunition clips, for example. That is certainly something he would be interested in looking at," he said.

These are all measures that have been vehemently opposed in the past by the NRA, which has used its lobbying muscle at federal and state level to both fight off any attempts to regulate gun ownership and to unwind existing controls.

But Tuesday's statement suggests a possible shift. The promise of meaningful contributions to ensure this never happens again is a long way from the NRA reaction to earlier massacres, detailed on Tuesday by Slate's Dave Weigel. The usual response is to express condolences and offer no concessions, or to express condolences and promise discussion at an "appropriate" time.

After the Virginia Tech shooting in 2007 that left 32 dead, the single worst gun incident in recent US history, it said: "The NRA joins the entire country in expressing our deepest condolences to the families of Virginia Tech University and everyone else affected by this horrible tragedy. Our thoughts and prayers are with the families."

When Congresswoman Gabby Giffords was shot last year in Tucson, Arizona, the NRA said: "At this time, anything other than prayers for the victims and their families would be inappropriate."

In July this year, after the massacre at the cinema in Aurora, Colorado, the NRA response was: "We believe that now is the time for families to grieve and for the community to heal. There will be an appropriate time down the road to engage in political and policy discussions."

But the response this time has been different. The NRA has never before faced such an outpouring of outrage.

The length of the delay in responding suggests the NRA has had difficulty framing its reaction this time. While so often indifferent to pressure from outside, it may be facing internal pressure from at least some of its members.

Democratic senator Joe Manchin, one of the strongest supporters of the NRA and gun rights but who now says he is open to reform because of Newtown, said he has been in touch with friends in the organisation. He spoke with Obama on Tuesday, the White House said.

Obama was "is heartened … by what we have all heard from some members of Congress who have been longtime opponents of gun control measures", Carney said.

The NRA, which has 4.3 million members, spent $24m during the election this year, much of it in support of pro-gun legislators. The only legislation the NRA has failed to block was the ban on automatic weapons in 1994, but the Bush administration allowed that to lapse in 2004.

In spite of this, gun control groups claim its power is exaggerated and can be broken, and are hoping that Newtown might be the catalyst for real change.

A few Republicans too have shown signs of movement this week. On Tuesday, Senator Lindsey Graham echoed Carney, saying that restrictions on the size of clips were worth looking at.

The Brady Campaign to Prevent Gun Violence brought victims of gun violence to Washington on Tuesday to face down the gun lobby, in particular the NRA. More than 20 members of families who lost people in shooting incidents or were wounded in them met members of Congress.

In the letter to Congress signed by the families, they wrote: "We know we are far from alone in our grief. Every day in America, 32 more families lose loved ones to gun murders, most in tragedies that do not make national headlines because they are so common. We believe we are better than this," the letter said.