Iran on Monday led calls by non-aligned nations for Israel to give up its nuclear weapons as a major conference got underway on advancing prospects for a nuclear-free world.

Iranian Foreign Minister Mohammad Javad Zarif addressed the conference on the nuclear Non-Proliferation Treaty (NPT) ahead of a meeting with US Secretary of State John Kerry on the landmark nuclear deal reached this month.

Zarif insisted that the 120-nation Non-Aligned Movement (NAM) is demanding that "Israel, the only one in the region that has neither joined the NPT nor declared its intention to do so, (...) renounce possession of nuclear weapons."

Israel is considered a nuclear-armed state although it has never acknowledged its status and has refused to join the NPT, a treaty that imposes obligations on signatories.

Israel is sending an observer to the month-long NPT conference for the first time in 20 years.

Zarif said non-aligned nations are also seeking "as a matter of high priority" to set up a nuclear-free-weapons zone in the Middle East.

The planned zone was agreed at the previous conference in 2010, but there was no action on the proposal.

- Back to the Cold War -

The 190 signatories of the NPT opened a month-long conference to review progress over the past five years in reducing the nuclear threat with much of the focus centered on the fate of US and Russian stockpiles.

UN chief Ban Ki-moon implicitly criticized the United States and Russia for failing to advance nuclear disarmament, a setback he said marked a return to a Cold War mindset.

In a speech delivered by his deputy Jan Eliasson, Ban said a nuclear-free world was the "historic imperative of our time."

"I am deeply concerned that over the last five years this process seems to have stalled," the UN leader said.

The secretary-general complained that instead of stepping up nuclear disarmament "there has been a dangerous return to Cold War mentalities."

Since it entered into force in 1970, the world has seen a drastic cut in warheads, but UN officials have raised alarm over the failure to move toward deeper cuts.

The United States and Russia have made little headway in reducing stockpiles since 2011, and the crisis over Ukraine is stoking distrust, dimming prospects for future cooperation.

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.

Ban said the action plans agreed at the last conference must be implemented, or the NPT "could risk fading in relevance."