Two days of talks between Iran and the European Union in Berlin have ended without agreement on how to resolve the dispute about Iran's nuclear programme.
Talks could resume by phone in the middle of next week
But both sides reported progress and said they would talk again. The EU's Javier Solana said talks would be held next week, possibly by phone.
Incentives are being offered to Iran to halt what some in the West believe is a bid to acquire nuclear weapons.
Threatened with UN sanctions, Iran says it wants only peaceful nuclear power.
Iranian negotiator Ali Larijani said positive conclusions had been reached at the talks in Berlin.
"It has been a long, constructive negotiation," he told reporters.
"Today we have discussed modalities with the aim of coming back to the main negotiations as soon as possible."
Speaking at the same news conference, Mr Solana said the sides had been "progressing".
"We will have a new contact in the middle of next week," he added.
If Iran does not suspend uranium enrichment, the US and the so-called EU3 - France, Germany and the UK - have agreed to ask the UN Security Council to impose sanctions.
Iran missed a Security Council August deadline to halt enrichment. President Mahmoud Ahmadinejad maintains Iran has a right to a nuclear programme.
China and Russia, two permanent members of the Security Council, are opposed to sanctions.