Iran will no longer share CCTV footage from its nuclear sites with the International Atomic Energy Agency, state media reported as the head of the UN body arrived for talks.
The nuclear watchdog's chief, Rafael Grossi, arrived overnight on Saturday for the first talks since Ebrahim Raisi, Iran’s new hardline president, took office.
Mr Grossi is seeking to ease tensions between Iran and the West that have risked scuppering the talks to remove US sanctions in exchange for Iran returning to compliance with a 2015 nuclear deal signed with world powers.
The IAEA and Iran's envoy to the agency said Mr Grossi would meet the new head of the Atomic Energy Organisation of Iran, Mohammad Eslami.
The IAEA informed member states this week that there had been no progress on two key issues: explaining uranium traces found at several old, undeclared sites and getting urgent access to monitoring equipment so that the agency can continue to keep track of parts of Iran's nuclear programme.
Earlier this month, the IAEA in a report said that Iran has continued to increase its stockpile of highly enriched uranium.
It also said that verification and monitoring activities had been “seriously undermined” since February, after Iran refused to let inspectors access IAEA monitoring equipment.
Mr Raisi has insisted that his country is being "transparent".
Iran previously shared surveillance footage from its nuclear sites with the IAEA and extended the arrangement temporarily in May, after an agreement lapsed, before cutting off access a month later.
Iran’s Press TV tweeted that the footage would not be shared and that an “informed source rejects reports suggesting that Iran may reconsider [its] decision on IAEA access restrictions."
Separate, indirect talks between the US and Iran on both returning to compliance with the 2015 deal have been suspended since June.
Washington and its European allies have urged Mr 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.
Then president Donald Trump pulled the US out of the deal in 2018, reintroducing painful economic sanctions.
Iran responded starting in 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.
Countries on the IAEA board of governors will be watching Mr Grossi's visit to see whether Iran yields either on granting access to the monitoring equipment, or if it offers the prospect of answers on the uranium particles found at the undeclared former sites.