Nuclear powers join non-nuclear nations on Monday to launch a conference on non-proliferation, buoyed by the Iran deal but alarmed by slow-moving US-Russian disarmament.

US Secretary of State John Kerry will address the conference that reviews the nuclear Non-Proliferation Treaty (NPT) and he may meet on the sidelines to discuss the hard-fought Iran deal with Foreign Minister Mohammad Javad Zarif.

Work on the framework Iran agreement must be completed by June 30 but it is already earning praise as a potential happy ending to one of the world's most vexing nuclear disputes.

Despite applause for the Iran deal, delegates from more than 150 countries are heading into the month-long conference with a sense of gloom over the lack of progress on disarmament and the deadlocked plan for a nuclear weapons-free zone for the Middle East.

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.

"We have a stalling in the path to a nuclear-free world," Angela Kane, the UN high representative for disarmament affairs, said ahead of the gathering at UN headquarters in New York.

Former Australian foreign minister Gareth Evans, who chaired the international commission on the NPT, described the state of play as "one of paralysis, of minimal forward-movement and of backsliding."

- Grand bargain -

Reached in 1968, the NPT is seen as a grand bargain between five nuclear powers -- Britain, China, France, Russia and the United States - 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 and the global consensus on how to move toward a nuclear-free world is under severe strain.

"The nuclear-weapons states are not living up to their side of the bargain," Kane said.

"Right now, the non-nuclear states need to be given the sense that they are taken seriously."

Delegates to the NPT conference are working on an "outcome document" laying out priorities for the next five years, but some diplomats have not ruled out that disagreements could lead to a collapse of the talks.

Pessimism has also focused on Washington's $1 trillion modernization plan for its nuclear forces that is compounding fears that the United States is not seriously working toward reducing its stockpile.

Another point of contention is a proposed nuclear weapons-free zone for the Middle East that has failed to materialize despite a plan at the last NPT conference to begin talks on the proposal in 2012.

Kane warned that the next five years will be crucial to ensure that the NPT "retains credibility."

She suggested that there be a roadmap with targets that are "not far off in Never-Never-Land" to reassure non-nuclear states that they have signed on to a treaty that is "worthwhile."

As a stark reminder of the horrors of a nuclear attack, a group of aging Hiroshima survivors are traveling to New York to attend the conference and make a personal appeal for action.