Nuclear discussions between Iran and six world powers are advancing in a good atmosphere but progress is "slow and difficult", a senior Iranian diplomat has said.
The remarks from Abbas Araqchi, a leading member of Iran's negotiating team at talks being held in Vienna, were carried Friday by the ISNA news agency.
"It's a good atmosphere and discussions are moving forward in a spirit of goodwill, but they are moving very slowly and with difficulty," he said.
The talks in Vienna, aimed at securing a permanent deal on the extent of Iran's nuclear activities, started Wednesday but there has been little indication of how they have gone so far.
Michael Mann, the spokesman for Catherine Ashton, the EU foreign policy chief and the six powers' lead negotiator, said in a tweet that the discussions would resume Friday.
After three earlier rounds of talks, this time Iran and the five permanent members of the UN Security Council plus Germany aim to start drafting the actual text of what could be a landmark agreement.
Britain, China, France, Russia, the United States and Germany want Iran to radically scale back its nuclear activities, making any dash for an atomic bomb virtually impossible and easily detectable.
Success could help Tehran and Washington normalise relations 35 years after the Islamic revolution toppled the US-backed Shah but failure could spark conflict and a regional nuclear arms race.
The parties want to get a deal by July 20, when a November interim deal under which Iran froze certain activities in return for some relief from crippling Western sanctions expires.
This could be extended but time is of the essence with hardliners on both sides -- members of the US Congress and arch-conservatives in Iran -- sceptical of the process and impatient for progress.
In return the Islamic republic, which denies seeking an atomic weapon, wants the lifting of all UN and Western sanctions, which have caused its economy major problems.