After silence spurred suggestion that gun group was too busy to oppose treaty, activists step up opposition as conference opens

The National Rifle Association is stepping up its opposition to a UN treaty aimed at halting the illicit trade of guns into conflict zones, after months of silence on the issue believed to be due to its focus on domestic gun control.

Human rights campaigners said that the resurgence of the NRA's campaign was designed to "stir up anti-UN panic" ahead of the UN conference on the Arms Trade Treaty, which opens on Monday in New York. The Obama administration indicated in a statement on Friday that it would sign the pact.

For years, the NRA has painted the UN as a bogeyman figure, claiming in its literature and fundraising drives that there is an international conspiracy to "grab your guns". Last July, when negotiations on the Arms Trade Treaty broke down – in part because of US resistance to global regulations on gun sales – the gun lobby group claimed victory for "killing the UN ATT".

Supporters of the treaty accuse the NRA of deceiving the US public about the pact, which they say will have no impact on US domestic gun ownership as it applies only to exports.

Michelle Ringuette, chief of campaigns and programs at Amnesty International USA, said they had witnessed a resurgence in the NRA's attempts to influence lawmakers and to use its opposition to the UN treaty as an opportunity for fundraising.

"We monitor what they send out to membership and put online" Ringuette told the Guardian. "It's nothing like the efforts they put in back in June and July but we have seen them step up. They have done exactly what we expected them to do, to stir up anti-UN panic."

Human rights campaigners say that it will have no impact on domestic regulations of firearms. It is aimed at stopping illegal trafficking of weapons, including small arms such as the AK-47 assault rifle, from pouring into conflict zones and fuelling wars and atrocities.

A report by the American Bar Association last month, which examined whether the arms treaty would impinge on the Second Amendment, concluded that "the proposed ATT is consistent with the Second Amendment … the treaty would not require new domestic regulations of firearms."

The Obama administration, in a statement on Friday endorsing the treaty, has said it will not sign anything which affects US Second Amendment rights.

The NRA, which founded the World Forum on Shooting Activities – an international coalition of manufacturers and gun rights activists which plans to speak out against the pact – has said that the treaty would be used to regulate "civilian weapons" and could infringe on US gun rights.

Tom Mason, the NRA's executive secretary and a lawyer who has represented the NRA at UN meetings for two decades, told the Washington Post on Sunday: "What we really object to is the inclusion of civilian firearms within the scope of the ATT."

"This is a treaty that really needs to address the transfer of large numbers of military weapons that leads to human rights abuses. We have submitted language that you can define what a civilian firearm is."

Ringuette said that the idea there was a classification of "civilian weapons" in the pact was "a fiction".

Any designation of civilian weapons would create an opportunity for arms dealers to say they were only dealing in civilian arms, she said, but the treaty had been carefully crafted "not to permit any such loopholes".

She accused the NRA of "carrying the water" for gun manufacturers and said they were using opposition to the pact as a "fundraiser".

"They are under siege on the domestic front. They are shouting from every side of their mouths."

According to the Small Arms Survey, roughly 650m of the 875m weapons in the world are in the hands of civilians. That, arms control advocates say, is why any arms trade treaty must regulate both military and civilian weapons.

Scott Stedjan, of Oxfam America described the NRA's opposition to the treaty as "irrelevant". "They know that arms treaty is not going to impact domestic gun control" he said. "The issue they are most concerned about lies outside the treaty."

Stedjan said that when the NRA speak out at the UN, other countries were puzzled by their approach.

"This treaty is not about this issue but it is about getting the support of their (NRA) grassroots," he said.

In a statement issued on Friday, secretary of state John Kerry said: "The United States is steadfast in its commitment to achieve a strong and effective Arms Trade Treaty that helps address the adverse effects of the international arms trade on global peace and stability."

"We will not support any treaty that would be inconsistent with US law and the rights of American citizens under our constitution, including the Second Amendment."