Iranian President Hassan Rouhani says the first step to talks with US President Donald Trump would be the removal of sanctions, decreasing the likelihood of a meeting.
Mr Trump appeared to confirm his willingness to talk with Iran at the G7 summit in Biarritz, south-west France, saying he would meet Mr Rouhani if the situation were right.
"If the circumstances were correct, I would certainly agree to that," he said on Monday, with clarifying what those circumstances would be.
But on Tuesday, Mr Rouhani told state TV that the first step was to drop the sanctions.
"You must retreat from all illegal, unjust and wrong sanctions against the nation of Iran," he said.
Iranian Foreign Minister Javad Zarif said the prospects for such a meeting were "unimaginable" without Washington rejoining the nuclear deal with Tehran.
Mr Zarif was speaking two days after he made a surprise trip to Biarritz for talks on the sidelines of the G7 summit.
Tension between Washington and Tehran has increased in recent months.
The Iranian economy has been struggling since the US reimposed sanctions after pulling out of a pivotal 2015 nuclear deal that put limits on Tehran's uranium enrichment programme.
Mr Zarif was invited to the G7 summit by host France, which has taken the lead in trying to ease tension between Tehran and the US.
It was initially reported that the unexpected arrival had angered Mr Trump and that he had not been told of the invitation.
But Mr Trump later said he knew about the invitation and "respected the fact that he was coming in. We're looking to make Iran rich again, let them be rich, let them do well, if they want".
Mr Rouhani also said that Iran would continue to scale back its nuclear commitments if the sanctions were not lifted.
"Tehran has never wanted nuclear weapons," he said. But he said that the country was always ready to hold talks.
The two countries have also been at loggerheads over the Grace 1 supertanker, which has now been renamed the Adrian Darya-1.
The Grace 1 was released from custody in Gibraltar this month, after being held for five weeks, as it was suspected of carrying oil to Syria in breach of EU sanctions.
The US Federal Court ordered the seizure of the vessel, claiming that it had links to the Iranian Islamic Revolutionary Guard Corps, which Washington has designated a terrorist organisation, soon after the detention order was lifted. The petition was rejected by Gibraltar.
Iran said any US move to seize the vessel again would have "heavy consequences".
It is not known where the tanker is going. It was initially sailing for Greece after its release and then Turkey.
It was revealed on Monday that the oil on board had been sold to an unidentified buyer.
Also on Monday, Iran said it sent destroyer Sahand to the Gulf of Aden, near Yemen, where the UAE and Saudi Arabia have been fighting the Iranian-backed Houthi rebels since 2015.