A month-long conference at the United Nations to decide on an action plan for nuclear disarmament headed into a final stretch on Wednesday with no agreement in sight.

More than 150 countries are taking part in the conference ending Friday on reviewing the nuclear Non-Proliferation Treaty, a landmark document that seeks to prevent the spread of nuclear weapons and technology.

Talks have been deadlocked over demands by non-nuclear states for concrete steps from nuclear powers to reduce their arsenals and provide annual reports on the state of their stockpiles.

An Austrian-led initiative backed by 159 states to ban nuclear weapons altogether has come up against strong resistance by the declared nuclear powers: Britain, China, France, Russia and the United States.

The conference president, Algerian Ambassador Taous Feroukhi, told delegates that "the gap is still wide" on disarmament and called for "an extra effort" to reach a consensus.

"Efforts are ongoing and I hope, I hope that we can arrive at something," said Feroukhi.

Delegates have been instructed to go back to the drawing board to come up with an acceptable draft to both nuclear powers and non-nuclear nations by Thursday 1900 GMT.

Kingston Reif, director for disarmament at the Arms Control Association, said he was not optimistic about chances for agreement on a final document, but that would not mean that the NPT is unraveling.

"Even if there is no consensus at this review conference, it doesn't mean that suddenly states are going to start leaving the NPT and there will be a cascade of proliferation and more nuclear weapons state," Reif told AFP.

But the rift would signal that non-nuclear states will be looking for other venues to make their demands on disarmament heard, he said.

- Not enough -

The NPT review conference failed to yield an action plan when it was convened in 2005, and disarmament activists complain that the measures agreed in the 2010 document have not been implemented.

"We know that even if there is a document, it's not going to be a very good one," said Beatrice Fihn, executive director of the Swiss-based International Campaign to Abolish Nuclear Weapons.

The month-long conference has shown that "it's difficult to reconcile the strong movement forward from non-nuclear states, and nuclear states that basically won't commit to anything," said Fihn.

Reached in 1968, the NPT is seen as a grand bargain between the five nuclear powers and non-nuclear states which agreed to give up atomic weapon ambitions in exchange for disarmament pledges.

But 45 years after the NPT entered into force, non-nuclear states are feeling increasingly frustrated about the slow pace of disarmament.

In particular, the United States and Russia have made little headway in cutting their nuclear stockpiles since 2011, and the crisis over Ukraine is stoking distrust, dimming prospects for future cooperation.

Talks on creating a weapons-free zone in the Middle East have run into problems after Russia put forward a proposal to hold a conference in 2016, under UN auspices, a diplomat said.

Israel, which is not a member of the NPT but is attending as an observer, is opposing the proposal, according to a diplomatic source.