The Harper government faced sharp criticism Wednesday for its continued refusal to sign a landmark treaty to regulate the global arms trade.

A group of non-governmental agencies, called the Control Arms Coalition, said it was frustrated and disappointed that the government did not follow the United States and more than 90 other countries in signing the Arms Trade Treaty.

Meanwhile, the federal NDP accused the government of indulging in conspiracy theories because it continues to express concern that the treaty might have an impact on lawful gun owners within Canada.

The criticism was unleashed after U.S. Secretary of State John Kerry signed the treaty on behalf of the U.S. on the sidelines of the United Nations General Assembly.

Kerry called it a "significant step" in keeping the world safe.

And he shot back at political opponents, saying that the treaty would have no effect on domestic gun ownership inside the U.S., where there is strong concern that it could violate the cherished rights of Americans to bear arms.

"This treaty will not diminish anyone's freedom," Kerry said, adding that the U.S. "would never think about supporting a treaty that is inconsistent with ... the rights of American citizens to be able to exercise their guaranteed rights under our Constitution."

Gun owners holding up Canada?

Kerry's view appears to differ sharply from those expressed by the Harper government on the issue.

Foreign Affairs Minister John Baird has said there is a potential link between signing on to the treaty and Canada's now-abolished long gun registry.

Baird's spokesman said the government is still doing consultations on whether the treaty would affect lawful recreational firearms owners in Canada.

"If properly done, an Arms Trade Treaty can help limit the worldwide trade in illicit arms," said Rick Roth in an email to CBC News on Wednesday. "At the same time, it is important that such a treaty not affect lawful and responsible firearms owners nor discourage the transfer of firearms for recreational uses such as sport shooting and hunting."

Project Ploughshares is a member of the Canadian coalition, along with Oxfam Canada, Oxfam Quebec and Amnesty International.

"It is past time for Canada to get beyond spurious claims that the treaty will affect legal Canadian gun-owners and join the states that want to save lives by ending irresponsible arms transfers," said Ken Epps, senior program officer for Project Ploughshares, in a statement.

NDP foreign affairs critic Paul Dewar said he was shocked that the U.S., which has a much tougher gun lobby, has signed the treaty before Canada.

"The fact that the government continues to refuse to sign the treaty indicates a preference for conspiracy theories over the simple truth: this is a treaty that will help save the lives of millions of civilians around the world and it has no impact on domestic owners of firearms," Dewar said in an email.

"Today's signature by the United States just makes it more obvious that the Conservatives are making this decision based on gun-lobby ideology and not reality."

'Deeply disappointed'

Robert Fox, executive director of Oxfam Canada, urged the government to sign the treaty without delay.

"Every day, conventional arms are used to commit serious acts of violence against women and girls, including rape," Fox said in a statement.

"We are deeply disappointed that Canada has not signed the treaty as this undermines our ability to champion women's rights, peace and security."

Prime Minister Stephen Harper was at a United Nations panel on maternal and child health on Wednesday, while Baird was to expected to speak later in the day on the issue of the forced marriage of children.

It is not clear what impact the treaty would have in curbing the global arms trade, estimated at between $60 billion and $85 billion annually. Much will depend on which countries ratify it, and how stringently it is implemented once it comes into force.

The treaty will not control the domestic use of weapons in any country.

It prohibits the transfer of conventional weapons if they violate arms embargoes or if they promote acts of genocide, crimes against humanity or war crimes, and if they could be used in attacks on civilians or civilian buildings such as schools and hospitals.

The treaty covers battle tanks, armoured combat vehicles, large-calibre artillery systems, combat aircraft, attack helicopters, warships, missiles and missile launchers, and small arms and light weapons.

It would require ratifying country to establish national regulations to control the transfer of conventional arms and components and to regulate arms brokers.