Iran said Sunday nuclear talks with world powers this week will be "difficult," as Israel boosted its campaign against a possible deal that would bring Tehran some sanctions relief.

Negotiations between Iran and the so-called P5+1 -- Britain, France, the United States, Russia and China plus Germany -- restart in Geneva on Wednesday after the last round failed to seal a deal.

Top diplomats insisted they were closing in on an interim agreement that would see Iran curb or freeze parts of its nuclear programme for some relief from crippling sanctions.

But senior Iranian negotiator Abbas Araqchi, who is also deputy foreign minister, said "the next round of nuclear talks will be difficult," according to remarks carried by the official IRNA news agency.

"No agreement will be reached without securing the rights of the Iranian nation" on its nuclear programme and uranium enrichment, he added.

Israel and the West suspect Iran is pursuing a nuclear weapons capability alongside its uranium enrichment programme, which Tehran insists is entirely peaceful.

Israel has argued that Western powers can get a better deal if they maintain or even ratchet up the sanctions, which have exacted a heavy toll on Iran's economy.

Prime Minister Benjamin Netanyahu, who welcomed French President Francois Hollande to Israel on Sunday, said he would also discuss the matter with US Secretary of State John Kerry in Jerusalem on Friday.

"I hope we'll be able to convince our friends this week and in the following days to get a much better deal. It can be achieved," he said in a statement.

"Continuing to apply pressure (on Iran) and even increasing it can yield a much better diplomatic result."

Netanyahu told a joint news conference with Hollande: "I'm concerned, gravely concerned, that this deal will go through and in one stroke of the pen, it will reduce the sanctions on Iran -- sanctions that took years to put in place -- and in return for this, Iran gives practically nothing,"

Iranian President Hassan Rouhani, a reputed moderate elected earlier this year, has vowed to try to reassure the West over Iran's programme in order to secure the lifting of the international sanctions.

Iran has insisted, however, that it has the right to enrich uranium on its soil, a key sticking point in previous rounds of talks going back more than a decade.

"Not only do we see Iran's right to uranium enrichment as non-negotiable, but we do not see any need for it to be recognised by others, since it is an integral part of Iran's rights under the Non-Proliferation Treaty," Foreign Minister Mohammad Javad Zarif told ISNA news agency.

Kerry questioned that assertion last week, arguing that Iran's right to enrich depended on it providing assurances to the international community that it is not pursuing an atomic bomb.

'Our red line'

But Zarif said no one in the P5+1 had asked Iran to stop uranium enrichment, adding that "the full suspension of enrichment is our red line and we do not cross it".

The mooted deal has come under criticism from both sides, with hardliners in Iran opposed to any concessions to the West and the US Congress threatening further sanctions.

US President Barack Obama's administration wants to offer Iran some "modest" and "reversible" sanctions relief as part of an interim deal to bolster Rouhani's negotiators and buy time for reaching a comprehensive accord.

Zarif, for his part, said "all measures taken by all parties in the first phase are reversible, if no favourable result is achieved", while insisting he remained optimistic about reaching a deal.

The last round of talks, which saw the foreign ministers of the P5+1 hold marathon talks in Geneva, ended without an accord.

Kerry said Iran had baulked at an offer agreed upon by the P5+1, but Iran and Russia said French objections to a draft thrashed out by Tehran and Washington had scuppered an agreement.

France had cited concerns about the heavy water reactor Iran is building at Arak, which would generate plutonium as a by-product and give Tehran a second possible route to an atomic weapon.

Hollande, who arrived in Israel on Sunday for a three-day visit expected to be dominated by discussions on Iran, insisted his country "will not tolerate nuclear proliferation".

"As long as we are not certain that Iran has decided to give up on nuclear weapons, we will continue with all our demands and with sanctions."