Iran has given sweeping assurances to the U.N. nuclear watchdog that it will finally assist a long-stalled investigation into uranium particles found at undeclared sites and even re-install removed monitoring equipment, the watchdog said on Saturday.

The International Atomic Energy Agency and Iran issued a joint statement on IAEA chief Rafael Grossi's return from a trip to Tehran just two days before a quarterly meeting of the agency's 35-nation Board of Governors.

The statement went into little detail but the possibility of a marked improvement in relations between the two is likely to stave off a Western push for another resolution ordering Iran to cooperate, diplomats said. Iran has, however, made similar promises before that have yielded little or nothing.

"Iran expressed its readiness to ... provide further information and access to address the outstanding safeguards issues," the joint statement said. A confidential IAEA report to member states seen by Reuters said Grossi "looks forward to ... prompt and full implementation of the Joint Statement."

Iran is supposed to provide access to information, locations and people, Grossi told a news conference at Vienna airport soon after landing, suggesting a vast improvement after years of Iranian stonewalling.

Iran would also allow the re-installation of extra monitoring equipment that had been put in place under the 2015 nuclear deal, but then removed last year as the deal unraveled in the wake of the U.S. withdrawal from the deal in 2018 under then-President Donald Trump.

Follow-up talks in Iran between IAEA and Iranian officials aimed at hammering out the details would happen "very, very soon," Grossi said.

Asked if all that monitoring equipment would be re-installed, Grossi replied "Yes." When asked where it would be re-installed, however, he said only that it would be at a number of locations.