A four-week U.N. review conference on the Nuclear Non-Proliferation Treaty ended Friday without adopting a consensus document after negotiators failed to narrow differences over a proposal to make the Middle East a nuclear weapons-free zone.

The failure to produce an outline for actions for the next five years at the meeting, which took place in the 70th anniversary year of the atomic bombings of Hiroshima and Nagasaki, raised concerns that efforts to advance toward a world free of nuclear arms will lose momentum.

The conference president, Algerian diplomat Taous Feroukhi, admitted to a lack of consensus at a plenary meeting that was held after hours of delay. Citing “diverging expectations of state parties for a progressive outcome,” she said “it would be impossible for any single consensual document to possibly meet the highest aspirations of all parties.”

With the current meeting — held once every five years — not the first to close without adopting a final document, the conference’s effectiveness in promoting its agenda of disarmament, nonproliferation and the peaceful use of nuclear energy may be thrown into question.

At the plenary meeting, the proposal for a Middle East zone that would involve Israel — an undeclared but acknowledged nuclear power — was raised by a number of speakers.

Rose Gotemoeller, the U.S. undersecretary for arms control and security policy, rejected a plan to hold a conference on establishing such a zone by March 1 next year that had been contained in the final draft for an outcome document, with the idea having been put forward by the Russians.

She called it “an arbitrary deadline” and blasted Egypt and other states, saying they were not willing to let go of this and other “unrealistic and unworkable conditions” in the text.

Britain and Canada also criticized the conference deadline language in the final text.

Egyptian Ambassador Hisham Badr slammed the United States, saying it had “blocked” an agreement on the nuclear-free zone. It is “a sad day” for the NPT, he said, pointing out how three countries had blocked the agreement. “By blocking consensus, we are depriving the world — but especially the Middle East — of even one chance of a better future,” he added.

Mikhail Ulyanov, the Russian head of delegation, said it was a “shame that such an opportunity for dialogue had turned out to be missed, perhaps for a long time to come.”

In the closing days of the conference, some observers said nuclear “haves” and “have-nots” in the NPT framework were narrowing some differences over nuclear disarmament in working out a final document. But consensus was blocked over the issue of Israel, which is not party to the treaty but attended the review meeting as an observer for the first time in 20 years.

Along with many other participants at the plenary meeting, Japanese Deputy Foreign Minister Shinsuke Sugiyama expressed disappointment about the lack of a final document, saying it is “extremely regrettable that this conference was not able to adopt a consensus, a substantive document, though we seemed to have come quite near to do so.”

Japan attempted to include an invitation for world leaders to visit Hiroshima and Nagasaki in the document, but it was dropped in the face of opposition from China, which said Tokyo was trying to portray itself as a war victim.

Despite the failure to come up with an agreed-on document Sugiyama stressed that this did not change his country’s commitment to the credibility of the NPT regime. “It is not all lost,” he said, adding that Japan will host a series of meetings on disarmament issues in August in Hiroshima.

Beatrice Fihn, the executive director of ICAN, a nongovernmental organization, said the removal of references to Hiroshima and Nagasaki visits was regrettable. “The 70th anniversary is very important to highlight the suffering that happens if a nuclear bomb detonates, and it is not a power-politics issue or an attempt to rewrite history — we just want to make sure that the world knows what a nuclear bomb does when used,” she noted.

NPT review conferences have been held since 1975. The 2005 meeting also failed to produce a substantive consensus document. The treaty counts roughly 190 signatories.