Parties to the pact were holding a formal meeting in Vienna on Sunday from 2:30pm (1230 GMT), the European Union said on Saturday.
A hardliner, Ebrahim Raisi, won Iran's presidential election on Friday and will take office in early August, replacing pragmatist Hassan Rouhani.
But this is unlikely to disrupt Iran's effort under supreme leader Ayatollah Ali Khamenei, who has final say on all major policy, to restore the nuclear pact and be rid of tough US oil and financial sanctions.
Negotiations have been going on in Vienna since April to work out the nature and sequencing of steps Iran and the US must take on nuclear activities and sanctions to return to full compliance with the nuclear pact.
Washington under then-president Donald Trump left the deal in 2018, branding it too flawed to remove the risk of Iran developing nuclear weapons capability, and re-imposed sanctions on the Islamic Republic.
Iran has since breached the deal's strict limits on uranium enrichment. It has said its moves would be reversed if the US rescinded all sanctions.
"Bridging the gaps requires decisions that mainly the other party (Washington) has to take. I hope in the next round we will travel this short distance albeit a difficult one," Araqchi said.