Iran told the United States in talks last week it was ready to accept some limits on its uranium enrichment but needed watertight guarantees US President Donald Trump would not again pull the US out of a nuclear pact, a senior Iranian official said.
Iran and the United States are set to hold a second round of talks this weekend in Rome, a week after a first round of negotiations in Oman which both sides described as positive.
Trump, who has restored a "maximum pressure" campaign on Tehran since February, ditched a 2015 pact between Iran and six world powers in 2018 during his first term and reimposed crippling sanctions on Iran.
In the intervening years, Tehran has steadily overstepped the 2015 agreement's limits on its nuclear program, designed to make it harder to develop an atomic bomb.
Former US president Joe Biden, whose administration unsuccessfully tried to reinstate the 2015 pact, was not able to meet Tehran's demand for guarantees that no future US administration would renege on it.
Tehran has approached the talks warily, sceptical they could yield a deal and suspicious of Trump, who has repeatedly threatened to bomb Iran if it does not halt its accelerating uranium enrichment program, which Iran says is peaceful.
While both Tehran and Washington have said they are set on pursuing diplomacy, they remain far apart on a dispute that has rumbled on for more than two decades.
Tehran's red lines "mandated by Supreme Leader Ayatollah Ali Khamenei" could not be compromised in the talks, the official told Reuters, describing Iran's negotiating position on condition of anonymity.
He said those red lines meant Iran would never agree to dismantle its centrifuges for enriching uranium, halt enrichment altogether, or reduce the amount of enriched uranium it stores to a level below the level it agreed in the 2015 deal that Trump abandoned.
It would also not negotiate over its missile program, which Tehran views as outside the scope of any nuclear deal.
"Iran understood in indirect talks in Oman that Washington doesn’t want Iran to stop all nuclear activities, and this can be a common ground for Iran and the US to start a fair negotiation," the source said.
Iran said reaching a deal with the United States was possible if "they demonstrate seriousness of intent and do not make unrealistic demands".
Top US negotiator Steve Witkoff, in a post on X earlier this week, said Iran must "stop and eliminate its nuclear enrichment" to reach a deal with Washington.
Tehran has said that it is ready to work with the UN nuclear agency, which it sees as "the only acceptable body in this process", to provide assurances that its nuclear work is peaceful, according to the source.
The source said Araqchi had told the Americans that, in return for that cooperation, Washington should promptly lift sanctions on Iran's oil and financial sectors.