World powers will today urge Iran to accept their offer to ease some economic sanctions if it stops its most sensitive nuclear work, in talks aimed at calming tension.
The US, Russia, China, France, Britain and Germany met Iranian negotiators in the Kazakh city of Almaty today at the start of the second round of talks this year.
They are aiming to settle a decade-old dispute over Iran's nuclear work.
With an Iranian presidential election in June complicating decision-making in Tehran, there is little chance of a breakthrough, but Israel has indicted its patience with diplomacy is running out.
Israel has threatened to bomb Iran's nuclear facilities if it does not curb the activities the world powers suspect are aimed at making a nuclear bomb.
Without a conclusive deal in sight, Western diplomats are hoping for at least a serious discussion of specific points of their proposal, made at the last talks in February.
Iran has resisted international pressure, arguing its uranium enrichment is for peaceful purposes only and therefore should be allowed to continue, under international law.
Its negotiators arrived in Almaty with their own proposals, the Iranian media reported without giving any detail, and chief negotiator Saeed Jalili struck a defiant tone.
"We think our talks tomorrow can go forward with one word. That is the acceptance of the rights of Iran, particularly the right to enrichment," Mr Jalili said in a speech at an Almaty university yesterday.
World powers say Iran has relinquished that right by hiding its nuclear work from UN inspectors in the past and refusing to grant them full access.
Talks are expected to last through tomorrow. If they fail to produce sufficient progress, Western governments are likely to impose new economic sanctions, with the double aim of pressuring Iran while seeking to persuade Israel to hold back from any military action.
In Israel, Prime Minister Benjamin Netanyahu told visiting US senators that Iran's nuclear work must be stopped.
"We cannot allow a situation in which a regime that calls for our annihilation has the weapons of annihilation. And I think that must be stopped at all cost," he said on Thursday.
US President Barack Obama sought to cool tempers during a trip to Israel in March, saying diplomacy was the best option, but he alluded to the possibility of last-resort military action.
Experts say Iran would likely seek to keep diplomacy on track ahead of the election, in part to avert new sanctions, but without coming close to any deal.