Three diplomats who follow the International Atomic Energy Agency closely told Reuters that Grossi's trip before next week's meeting of the IAEA's 35-nation Board of Governors was confirmed. Two said he would meet the new head of the Atomic Energy Organization of Iran, Mohammad Eslami, on Sunday.
The IAEA and Iran's envoy to the agency later confirmed the trip and the meeting.
"Director General Rafael Mariano Grossi will meet with Vice-President of the Islamic Republic of Iran and Head of the AEOI, Mohammad Eslami, in Tehran on Sunday," the IAEA said, adding that Grossi was expected to hold a news conference at Vienna airport around 8:30 p.m. (1830 GMT) on Sunday.
The IAEA informed member states this week that there had been no progress on two central issues: explaining uranium traces found at several old, undeclared sites and getting urgent access to some monitoring equipment so the agency can continue to keep track of parts of Iran's nuclear programme as provided for by the 2015 deal.
Separate, indirect talks between the United States and Iran on both returning to compliance with the deal have been halted since June. Washington and its European allies have been urging hardline President Ebrahim Raisi's administration, which took office in August, to return to the talks.
Under the 2015 deal between Iran and major powers, Tehran agreed to restrictions on its nuclear activities in exchange for the lifting of sanctions.
President Donald Trump pulled the United States out of the deal in 2018, re-introducing painful economic sanctions. Iran responded as of 2019 by breaching many of the deal's core restrictions, like enriching uranium to a higher purity, closer to that suitable for use in nuclear weapons.
Western powers must decide whether to push for a resolution criticising Iran and raising pressure on it for stonewalling the IAEA at next week's meeting of the agency's 35-nation Board of Governors. A resolution could jeopardise the resumption of talks on the deal as Tehran bristles at such moves.
Iran's Foreign Ministry warned against any such resolution.
"I hope the Board of Governors, under the influence of certain pressures, will not take any action that would destroy the process of customary cooperation between Iran and the agency," said spokesman Saeed Khatibzadeh, the Fars news agency reported.
The European parties to the 2015 deal - Britain, France and Germany - held a meeting with the United States in Paris on Friday to discuss how to react at the IAEA board and to review options if Iran continues to stall on returning to negotiations. But diplomats said no decisions had been taken as of yet.
Countries on the IAEA Board of Governors will be watching Grossi's visit to see whether Iran yields either on granting access to the monitoring equipment to service it or offers the prospect of answers on the uranium particles found at the undeclared former sites.
Moves on those issues would make it less likely that a resolution is brought against Iran, diplomats say.