From Japan's "extreme regret" to Norway's "profound disappointment," delegates expressed frustration that the failure to agree on an action plan for growing nuclear threats might weaken the Nuclear Nonproliferation Treaty, the pact that has helped keep a lid on nuclear weapons for 35 years.
UN Secretary-General Kofi Annan said through a spokesman on Friday that the inability to strengthen collective efforts through the talks was bound to weaken the treaty.
Annan said world leaders would look at the issues again at a global summit scheduled for September.
Heightening nuclear tensions
The failure comes at a time of heightening nuclear tensions in the world. North Korea has pulled out of the treaty and says it is building atom bombs. Iran's uranium-enrichment programme raises questions about possible weapons plans.
Arab states view Israel's nuclear arsenal as increasingly provocative. The conference had debated proposals to address all these issues.
Many delegates were also disturbed over Bush administration talk of modernising the US nuclear force, and sought US reaffirmation of commitments made to disarmament steps at the nonproliferation conferences of 1995 and 2000.
"If we allow agreements at one conference to be rolled back at the next, we will undermine the very premise the multinational system is based upon"
Abdul Minty, South African diplomat
In this meeting's final hours, the US-led Western group of nations blocked any mention of those commitments in the conference's already-thin final report.
Every five years
The disagreements even kept conference president Sergio de Queiroz Duarte from issuing a statement endorsing nonproliferation principles. "It would be very difficult for me in the face of so many divergencies," the Brazilian diplomat told reporters.
Members of the 188-nation Nuclear Nonproliferation Treaty convene only once every five years to assess the workings of the 1970 treaty and find ways to make it work better - political commitments that give a boost to nonproliferation initiatives.
Under the nuclear pact, states without atomic arms pledged not to develop them, and five with the weapons -the United States, Russia, Britain, France and China -undertook to eventually eliminate their arsenals. The nonweapons states, meanwhile, were guaranteed access to peaceful nuclear technology.
Citing that guarantee, Iran has obtained uranium-enrichment centrifuges, which can produce both fuel for nuclear power plants and material for bombs. Washington contends Tehran plans to build weapons, but the Iranians say they are interested only in peaceful energy.
Delegations there had promoted ideas, for example, for limiting access to such dual-use technology with bombmaking potential, along with proposals to strengthen inspection of nuclear facilities and to pressure nuclear-weapons states to shrink their arsenals more quickly.
On treaty withdrawal, which North Korea managed without consequence under the nonproliferation pact, some delegations supported plans to make the process more difficult and penalty-laden.
But the dozens of proposals were stalled for more than two weeks while delegations squabbled over the agenda. Then, when debate finally started, it proved impossible to win consensus in committees.
Two issues debated were Iran
and North Korea's nuclear activities
Iran objected to any mention of it as a proliferation concern. Egypt balked at toughening treaty withdrawal, since it wants that option open as long as ex-enemy Israel has nuclear bombs. And the United States fought every reference to its 1995 and 2000 commitments.
Those commitments included, for example, activating the nuclear test-ban treaty and negotiating a verifiable treaty to ban production of bomb materials - both steps the Bush administration opposes, but other weapons states support.
In final speeches on Friday, delegation after delegation, including the European Union representative, spoke of the importance of the 1995-2000 commitments.
"If we allow agreements at one conference to be rolled back at the next, we will undermine the very premise the multinational system is based upon," said South Africa's Abdul Minty.
The lead US delegate, Jackie Sanders, countered that the United States has a "strong record on nuclear disarmament." She expressed only mild disappointment at the conference outcome, instead pointing to unilateral Bush administration initiatives to halt the spread of ultimate weapons, such as its efforts to intercept illicit nuclear trade.
In an interview with journalists from his Vienna headquarters, the UN nuclear agency head, Mohamed ElBaradei, said of the failed conference, "It is vital that we pick up the pieces and look forward. We have a golden opportunity at the summit meeting in New York" in September.
"It is vital that we pick up the pieces and look forward"
Mohamed ElBaradei, IAEA chief on the conference failure
As the conference closed, the UN spokesman's office said Annan "challenges leaders to use that (summit) opportunity to make bold commitments and address the pressing challenges."