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 scale back its nuclear activities. Success could help Tehran and Washington normalize relations 35 years after the Islamic Revolution toppled the US-backed Shah but failure could complicate the situation in the region. 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 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 -- skeptical of the process and impatient for progress.