United Nations ? A monthlong conference to toughen global controls on nuclear arms ended Friday with nothing to show for its four weeks of divisive work.

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 doomsday weapons for 35 years.

U.N. Secretary-General Kofi Annan believes “their inability to strengthen their collective efforts is bound to weaken the treaty,” his spokesman said. Annan said world leaders should deal with the issues at a global summit scheduled here for September.

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 program raises questions about possible weapons plans. Arab states view Israel’s nuclear arsenal as increasingly provocative.

The conference had futilely debated proposals to address all these issues.

Many delegates also were disturbed about the Bush administration’s talk of modernizing the U.S. nuclear force, and sought U.S. reaffirmation of commitments made to disarmament steps at the nonproliferation conferences of 1995 and 2000.

In this meeting’s final hours, the U.S.-led Western group of nations blocked any mention of those commitments in the conference’s already-thin final report.

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 divergences,” the Brazilian diplomat said.

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.

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 fuel for nuclear power plants and material for bombs.