U.N. member states have failed to reach agreement on a new treaty to regulate the multibillion-dollar global arms trade.

Some diplomats and treaty supporters blamed the United States for triggering the unraveling of the month-long negotiating conference.

Hopes had been raised that agreement could be reached on a revised treaty text that closed some key loopholes by Friday's deadline for action. But the United States announced Friday morning that it needed more time to consider the proposed treaty -- and Russia and China then also asked for more time.

A bipartisan group of 51 U.S. senators on Thursday had threatened to oppose the global treaty regulating international weapons trade if it falls short in protecting the constitutional right to bear arms.

In a letter to President Obama and Secretary of State Hillary Clinton, the senators expressed serious concerns with the draft treaty that has circulated at the United Nations, saying that it signals an expansion of gun control that would be unacceptable.

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The Constitution's Second Amendment offers broad protection for weapons ownership by civilians. As recently as 2008, the Supreme Court affirmed it when it struck down a ban on handguns in the District of Columbia, ruling that individuals have a constitutional right to keep guns for self-defense and other purposes.

The court also has ruled separately that treaty obligations may not infringe on individual constitutional protections and rights within U.S. borders. This goes back at least to a 1920 ruling that a migratory bird treaty with Canada, which prohibited the hunting or capturing of certain birds, was an unconstitutional interference with states' rights under the 10th Amendment.

Treaties are government-to-government agreements and do not subject citizens of one nation to laws of another or to those of an outside body.

Also, the U.N. resolution that authorized drafting of the small arms treaty recognizes the clear-cut right of nations "to regulate internal transfers of arms" and says nothing in the treaty that emerges will affect "constitutional protections on private ownership" of firearms.

Beyond that, there are many court rulings spelling out the limits of treaties. And if an act of Congress is inconsistent with a treaty obligation, the law passed by Congress prevails. Legal scholars say this has been well established.

The U.N. General Assembly voted in December 2006 to work toward a treaty regulating the growing arms trade, with the U.S. casting a "no" vote. In October 2009, the Obama administration reversed the Bush administration's position and supported an assembly resolution to hold four preparatory meetings and a four-week U.N. conference in 2012 to draft an arms trade treaty.

The United States insisted that a treaty had to be approved by the consensus of all 193 U.N. member states.

Ambassador Roberto Garcia Moritan, the conference chairman, said treaty supporters knew "this was going to be difficult to achieve" and there were some delegations that didn't like the draft though "the overwhelming majority in the room did." He added that some countries from the beginning of negotiations had "different views" on a treaty, including Syria, Iran and North Korea.

Despite the failure to reach agreement, Moritan predicted that "we certainly are going to have a treaty in 2012."

He said there are several options for moving forward in the General Assembly which will be considered over the summer, before the world body's new session begins in September.

Britain has taken the lead in pushing for a treaty to reduce the impact of the illicit arms trade.

Ahead of Friday's meeting, Britain's Deputy Prime Minister Nick Clegg discussed treaty prospects with U.N. Secretary-General Ban Ki-moon in London and told reporters and both urged the treaty's adoption.

"Global rules govern the sale of everything from bananas to endangered species to weapons of mass destruction, but not guns or grenades," Clegg said. "This anomaly causes untold suffering in conflicts around the world. 1,000 people are killed daily by small arms wielded by terrorists, insurgents and criminal gangs."

The secretary-general said he was disappointed at the failure to agree on a treaty, calling it "a setback." But he said he was encouraged that states have agreed to continue pursuing a treaty and pledged his "robust" support.

At the end of the negotiating session, Mexico read a joint statement from more than 90 countries saying they "are determined to secure an Arms Trade Treaty as soon as possible."