Nuclear chiefs have failed to agree new measures to stop weapons proliferation after a month of talks in New York.
Iran and North Korea are accused of seeking to develop weapons
Delegates from 188 nations had been discussing ways to beef up the Nuclear Non-Proliferation Treaty (NPT), which first came into force in 1970.
The accord aims to stop the spread of nuclear weapons, achieve disarmament and promote nuclear energy.
But even amid international concerns about nuclear activities in Iran and North Korea, no deal was struck.
Politics and procedural wranglings dogged the planned review of the treaty from the start, the BBC's Jonathan Marcus reports from the UN headquarters in New York.
He adds that it is hard to see the conference as anything other than a lost opportunity to bolster the NPT.
"I regret that the conference has not reached consensus," conference chairman Brazilian Sergio Duarte told the delegates on the final day of the talks.
GLOBAL NUCLEAR POWERS
Signed the NPT: US, Russia, UK, France, China
Declared or known: India, Pakistan, Israel
Suspicions over: North Korea, Iran
Formerly had programmes: Algeria, Argentina, Belarus, Brazil, Kazakhstan, Iraq, Libya, Romania, South Africa, Ukraine
Three separate committees had been discussing the three key areas that the treaty covers - nuclear disarmament, safeguards on national nuclear programmes and the peaceful use of atomic energy.
Arms control advocates say the US delegation came intent on focusing on the proliferation side of the equation and was totally unwilling to give any ground on US pledges to scrap its nuclear arsenal, our correspondent says.
The delegates also wasted two weeks of the talks arguing on empty procedural wrangling, he says.
In recent months the US and Iran in particular have been at loggerheads over Tehran's nuclear activities.
Washington accuses Iran of using its nuclear energy programme as a cover for developing nuclear weapons - a charge Tehran denies.
When the talks began in May, UN Secretary General Kofi Annan called on world leaders to reinforce their commitment to a treaty and for former Cold War rivals Russia and the US to reduce their current nuclear arsenals.
Mr Annan warned then of the possibility of a nuclear catastrophe.
"In our interconnected world, a threat to one is a threat to all, and we all share responsibility for each other's security," he said.
"The plain fact is that the regime has not kept pace with the march of technology and globalisation, and developments of many kinds in recent years have placed it under great stress."
ESTIMATED NUCLEAR WARHEADS, STRATEGIC AND TACTICAL
*The US is also said to have some 3,000 warheads in reserve, while Russia has about 11,000 in non-operational stockpiles
Israel declines to confirm it has nuclear weapons
North Korea claims it has nuclear arms but no details are available
Iran is accused by the US of ambitions to build nuclear arms