GENEVA: Iran's supreme leader vowed Wednesday no retreat from Tehran's nuclear “rights” in an anti-Israel diatribe that France said “complicates” talks underway in Geneva.

Predicting the demise of “rabid dog” Israel, which Iran has accused of trying to “torpedo” a deal, Ayatollah Ali Khamenei said world powers must respect the Islamic republic's “red lines”.

“I insist on not retreating one step from the rights of the Iranian nation,” Khamenei, 74, told militiamen of the Basij force in a live televised address.

France said that his comments on Israel, he called its leaders “not worthy to be called human” were “unacceptable and complicate negotiations” in Geneva.

Political directors from the US, China, Russia, Britain, France and Germany held talks on Wednesday afternoon before chief negotiator Catherine Ashton met Iran's Foreign Minister Mohammad Javad Zarif.

A plenary session of all the participants was due to start at 1700 GMT, according to Ashton's spokesman.

Hassan Rouhani's election as Iranian president in June raised hopes for an end to the standoff over Tehran's nuclear programme after a decade of failed initiatives and rising tensions.

But Israel, widely assumed to have a formidable nuclear arsenal itself, has expressed alarm at the mooted deal on the table in Geneva.

Instead of stopping all uranium enrichment, as multiple UN Security Council resolutions have demanded, the powers appear to be satisfied with a suspension of enrichment above five percent purity.

Along with other steps, this would be a “first-phase” suspension meant to build mutual confidence while the details of a longer-term accord are hammered out over following months.

Washington says this will “put time on the clock”, extending the time needed in theory by Iran to enrich enough weapons-grade uranium for a bomb.

For Israeli Prime Minister Benjamin Netanyahu, who arrived in Moscow on Wednesday where he sought to press Russian President Vladimir Putin to harden his stance, this leaves intact Iran's ability to make a bomb.

“You are not really dismantling any capacity to make fissile material for nuclear weapons,” he said in an interview published in top-selling German daily Bild on Tuesday.

Israel has refused to rule out bombing Iran, as it was assumed to have done with an Iraqi reactor in 1981 and a Syrian site in 2007. Iran says its programme is peaceful.

Uranium enrichment is the main worry for the international community since enriched uranium has civilian uses but also can go into a bomb.

Iran already has enough uranium stocks for several bombs if it chose to enrich it further to weapons-grade, a “breakout” that, for now, would be detected by the International Atomic Energy Agency, the UN watchdog.

Third time lucky

It remains to be seen whether Iran, seeking an easing of UN, US and EU sanctions that have more than halved the country's lifeblood oil exports, will accept the minor relief the P5+1 offering in return.

On the table, in the third meeting since Rouhani took office, is “limited, temporary, targeted and reversible” relief that a senior US official said “will not come anywhere near helping Iran escape the hole that we've put them in”.

“We will maintain the sanctions as long as we are not certain that Iran has definitively and irreversibly renounced its military programme to obtain nuclear weapons,” French President Francois Hollande said in Israel on Monday.

If Rouhani's “charm offensive” fails to secure quick and substantial relief from the sanctions, the Iranian president risks losing the support of arch-conservatives and, most importantly, that of the supreme leader, experts say.

Guarded optimism

Nevertheless Iran's foreign minister was upbeat about the prospects of reaching a deal in Geneva, 10 days after a previous, high-drama round in the same Swiss city came close but ultimately failed.

“I think there is every possibility for success,” Zarif, who also posted a conciliatory but defiant video message online on Tuesday, said on a stopover in Rome.

US President Barack Obama, fresh from seeking to dissuade lawmakers from imposing new sanctions on Iran, was more cautious on Tuesday: “I don't know if we will be able to close a deal this week or next week.”

Calling the talks a “historic opportunity”, British Foreign Secretary William Hague said in Turkey that the differences were “narrow and ... can be bridged through political will and commitment”.

German counterpart Guido Westerwelle said that the last round “showed that a diplomatic solution is possible ... At issue now is entering a first phase of confidence-building steps.”