An Iranian expert involved in nuclear talks with world powers, says the sessions have been useful but were "just the beginning".
Nuclear talks between experts from Iran and world powers have been useful, but more discussions are needed before a lasting deal can be reached, Tehran's team leader says.
"Fortunately, we reviewed many topics of the nuclear issue, but it is just the beginning and more sessions... will be needed," Hamid Baeedinejad, who lead the Iranian experts, told state broadcaster IRIB's website after the talks concluded on Friday.
Baeedinejad refrained from giving details, except to say they focused on uranium enrichment, the unfinished Arak heavy water reactor and nuclear cooperation.
"All the involved parties view the sessions as useful," Baeedinejad told the official IRNA news agency, saying the negotiations are "serious and substantive".
Experts from Iran and the P5+1 - Britain, China, France, Russia and the United States plus Germany - have been holding closed-door technical talks in Vienna since Wednesday.
Baeedinejad said a report on the talks will be submitted to the deputy foreign ministers of the participating countries, who are due to meet in Vienna in the next 10 days.
Western nations and Israel have long suspected Iran is covertly pursuing a nuclear weapons capability alongside its civilian programme, charges denied by Tehran.
The unfinished Arak reactor is of concern to the West because Tehran could theoretically extract weapons-grade plutonium from its spent fuel if it also builds a reprocessing facility.
A landmark interim deal reached in November requires that Iran freeze or curb its nuclear activities for six months in exchange for some sanctions relief while the two sides try to reach a comprehensive agreement.