Iran’s President Ebrahim Raisi and Russian leader Vladimir Putin spoke by phone on Tuesday before talks to revive a version of the 2015 nuclear deal.
The multinational talks held in Vienna, involving Russia, China, the EU, Britain and a US envoy, were paused after the election of Iranian President Ebrahim Raisi in June. They are set to recommence on November 29.
Shortly after the call was announced, The Wall Street Journal reported diplomatic sources said Iran was building new "advanced centrifuges" to enrich uranium at Karaj, a site where the International Atomic Energy Agency had previously been monitoring construction under the deal, from which Donald Trump withdrew in 2018.
It was not clear how the sources knew of renewed activity at the site. The IAEA has yet to comment on the allegations.
Karaj has been the centre of a row between Iran and the agency, which was allowed to monitor the site remotely with cameras until they were damaged in what Iran said was a sabotage attempt by a foreign power, in June.
An agreement between Iran and the IAEA in September would have allowed inspectors to reinstall cameras at the site, but the agency has since accused Iran of not giving them access.
The IAEA said lack of access was “seriously compromising” its efforts to verify Iran’s nuclear activities.
Meanwhile, China said it had “reached a broad consensus” with Iran and Russia on the nuclear deal, without giving more details.
The comments point to a united front between the three countries as world powers, including the EU, prepare for indirect talks between Iran and the US in Vienna.
Hopes of restoring the agreement have been dampened significantly since Mr Raisi was elected president and appointed a hawkish foreign policy team led by officials who have been highly critical of the nuclear deal.
The long-term foes have not been able to agree on how the US should return to the pact or how it could give Iran a guarantee that it would not back out again.
Russia has said it supports Tehran’s call for a guarantee against future US withdrawal and the removal of all sanctions that breach the original deal.
Mr Raisi told Mr Putin that Iran was ready to finalise a long-term co-operation agreement with Russia to strengthen economic ties.
That underscored efforts by Tehran to expand trade and strategic alliances with Russia and China in response to Washington’s withdrawal from the nuclear accord.