The EU's foreign policy chief has described as "constructive" talks with Iran's top nuclear negotiator.
Iran says its nuclear programme is for peaceful purposes only
Speaking after meeting Ali Larijani in Portugal, Javier Solana said another round of talks will be held next month.
Mr Larijani said Iran wanted a diplomatic solution to the dispute.
It comes a day after the UN's nuclear watchdog and Iran said they had agreed how to clear up questions about the nature of Iran's nuclear programme.
Iran is under pressure from the EU and US to suspend its nuclear programme and uranium enrichment activities.
They accuse the Islamic Republic of seeking to build nuclear weapons. Iran says its nuclear programme is entirely peaceful and is solely aimed at producing civilian nuclear power.
"We have had a very constructive meeting, and we will meet again in three weeks' time," Mr Solana said after the four-hour meeting in the Portuguese capital, Lisbon.
The talks come as permanent members of the UN Security Council consider tougher sanctions against Tehran over its refusal to give up uranium enrichment.
The Council first imposed sanctions on Iran in December for rejecting its demands, renewing them in March.
Mr Larijani warned that further sanctions could derail any negotiations towards a settlement.
"For [most] countries, the prevalence of tranquillity would be more important," he said.
Mr Larijani also said that he intended to address outstanding issues with the International Atomic Energy Agency (IAEA), but provided no details.
UN nuclear inspectors complain they have been stonewalled by the Iranian authorities.