World powers are set to begin two days of talks in Geneva with Iran on its controversial nuclear programme, but no major breakthrough is expected.
Iran’s foreign minister said he hoped a “roadmap” could be reached, describing the process as “time-consuming”.
Iran’s new President Hassan Rouhani, who is seen as a relative moderate, has said he wants a deal within six months.
The West suspects Iran is seeking to achieve a nuclear arms capability – a claim denied by Tehran.
Ahead of the talks, Israel warned that it would be a “historic mistake” to ease pressure on Iran.
The Iranian team is led by Foreign Minister Mohammad Javad Zarif, although much of the actual negotiating is expected to be delegated to his deputy, Abbas Araqchi.
“Tomorrow is the start of a difficult and relatively time-consuming way forward,” Mr Zarif posted on his Facebook page.
“I am hopeful that by Wednesday we can reach agreement on a roadmap to find a path towards resolution.”
These are the first such talks since President Rouhani took office in August, and this has raised hopes that a deal can be reached.
International negotiators say they are open to hearing Tehran’s ideas.
They want Tehran to take specific steps to prevent it from ever being able to make nuclear weapons, the BBC’s James Reynolds in Geneva reports.
In return, they promise to lift some of the international sanctions which have been imposed in recent years.
However, the West has hinted that it will be difficult to clinch a deal in just two days of talks.
“No-one should expect a breakthrough overnight,” said a senior US official, who was speaking on the condition of anonymity.
Western nations believe Iran’s uranium enrichment programme is covertly meant to achieve a nuclear arms capability.
Tehran says it wants only to master nuclear technology to generate electricity and carry out medical research.
Iran has been negotiating with the P5+1 group since 2006, because it wants the UN sanctions against it to be lifted.
Western negotiators have demanded that Iran halt the production and stockpiling of uranium enriched to 20% – a step away from achieving a nuclear weapons capability.
They also want Iran to send some of its stockpiles abroad, and shut down the Fordo production site near Qom where most of the higher-grade enrichment work is done.
But Mr Araqchi insisted on Sunday that there could be no question of Iran relinquishing its stockpiles of enriched uranium.
“We will not allow even a gram of uranium to go out of the country,” he said, quoted on the website of Iranian state TV.
On Monday, Israeli Prime Minister Benjamin Netanyahu said it would be wrong to ease pressure on Tehran.
Speaking in parliament, he said that any move to let up on the Iranian government would only strengthen its “uncompromising elements”, and Supreme Leader Ayatollah Ali Khamenei “will be perceived as the winner”.
In reference to the current international sanctions against Iran, he said it would be “a historical mistake to lift the sanctions, just before they are really effective”.
But in the US – which has also shown a tough stance against lifting sanctions on Iran – nine leading senators said they were open to the idea of suspending new sanctions if Tehran took significant steps to slow its nuclear programme.
In a letter to President Barack Obama, the senators emphasised that, in the meantime, the threat of military force should remain.