Foreign Minister Abbas Araqchi would be told that Iran must send a "clear signal", two diplomats told Reuters, with pressure mounting on Tehran to agree tough curbs on its nuclear program to prevent the potential development of an atomic weapon.
US Secretary of State Marco Rubio spoke to several Western counterparts before the meeting in Switzerland, the diplomats said, indicating readiness to engage directly with Tehran.
Washington did not confirm that though broadcaster CNN quoted a US official saying President Donald Trump supported diplomacy from allies that could bring Iran closer to a deal.
Tehran, however, has repeatedly said it will not talk to the Trump administration until Israeli attacks end.
The ministers from Britain, France and Germany, known as the E3, plus the European Union's foreign policy chief, were meeting separately on Friday before planned face-to-face talks with Araqchi.
"The Iranians can't sit down with the Americans whereas we can," a European diplomat said.
"We will tell them to come back to the table to discuss the nuclear issue before the worst-case scenario, while raising our concerns over its ballistic missiles, support to Russia and detention of our citizens."
The talks were due for mid-afternoon in Geneva, where an initial accord between Iran and world powers to curb its nuclear program in return for sanctions lifting was struck in 2013 before a comprehensive deal in 2015.
Separate talks between Iran and the US collapsed when Israel launched what it called Operation Rising Lion against Iran's nuclear facilities and ballistic capabilities on June 12.
"There is no room for negotiations with the US until Israeli aggression stops," Araqchi was quoted as saying on Iranian state TV on Friday.
The E3 have in past talks with Iran suggested it keep some uranium enrichment but accept extremely strict international inspections of its nuclear activities.
Trump has demanded zero enrichment and French President Emmanuel Macron appeared to echo that call on Friday, saying any new deal needed to go towards zero enrichment for Iran.
The main message Europeans will pass to Araqchi is that the US has signalled readiness for direct talks, but that Iran must give a serious signal, the two European diplomats said, without defining what the signal should be.
Trump's special envoy to the Middle East, Steve Witkoff, has spoken to Araqchi several times since last week, sources say.
While diplomats did not expect a breakthrough in Geneva, they said it was vital to engage with Iran because once the war stopped the nuclear issue would remain unresolved given that Tehran would still retain the scientific know-how.
Trump has said he will decide within two weeks whether to join Israeli strikes.
"A window now exists within the next two weeks to achieve a diplomatic solution," British Foreign Secretary David Lammy said.
