MONTREUX, Switzerland (AFP) — Israeli Prime Minister Benjamin Netanyahu yesterday sought to shoot down a nuclear deal being negotiated behind closed doors between Iran and world powers, warning it would leave Tehran free to develop atomic weapons.

But he did not reveal — as his aides had warned — specific details of the agreement shared with Israel in classified briefings by US officials.

Few insights into the comprehensive accord under discussion since November 2013 have leaked out, with officials remaining tight-lipped to protect the high-stakes negotiations.

But US officials did lay out late last week some of what they called the “bottom lines” of any deal, without going into specifics.

Here are some of the possible contours of a deal:

The goal

To reach a verifiable, comprehensive agreement that limits Iran’s ability to harness enough fissile material to build a nuclear bomb. In return, the international community would initially ease and then lift all sanctions imposed on the Islamic Republic.

Breakout time

World powers want to cut Iran’s ability to build an atomic weapon to a “one-year breakout time.” That would mean Tehran would need at least 12 months to be able to produce enough fuel for a nuclear bomb.

The assumption is that the international community would have enough time to detect such a move — and could seek to strike or destroy the facilities.

This year-long breakout time would stay in place for the length of the deal, which US officials have said they want to be in “double-digits”.

Many assume that this figure is pointing to a deal lasting about 10 years, but US officials have refused to comment.

Enrichment

This is one of the trickiest issues. Iran currently has about 19,000 centrifuges. About 10,200 centrifuges are in operation, used for spinning uranium gas at supersonic speeds to make it suitable for power generation and medical uses but also, at high purities, for a bomb.

According to documents leaked by the Israelis, and deemed accurate by non-proliferation experts, the US wants Tehran to reduce its total number of centrifuges to between 6,500-7,000.

Under the 2013 interim deal, Iran has halted production of 20 per cent highly enriched uranium and eliminated or diluted much of its stock down to just five per cent in return for limited sanctions relief.

Negotiators now seek to enshrine that agreement and cut Iran’s stockpile of low-enriched uranium gas. A senior US official said Tehran would have to “significantly reduce” both the number of centrifuges and its uranium stocks.

There may also be a proposal allowing Iran to ship its uranium gas to Russia, which would convert it to fuel rods for the Bushehr nuclear plant which Moscow helped build.

Nuclear plants

A senior US administration official said last week Iran should not be allowed to develop weapons-grade plutonium at its unfinished Arak reactor.

Plutonium can be used as an alternative fissile material to highly enriched uranium.

“We’re discussing how Iran can convert that Arak reactor to serve a different purpose,” the official said.

Iran should also not use its Fordo nuclear plant to enrich uranium, which would leave only its Natanz plant capable of enriching uranium.

Monitoring

A tough inspection programme using UN watchdog, the IAEA, is a cornerstone of any deal to allay any fears that Iran could covertly develop a nuclear arsenal. The US bottom line is that Iran must agree to unprecedented inspections of both nuclear and production facilities as well as uranium mines and mills and suspect sites.