Ali Akbar Salehi, the head of Iran's Atomic Energy Organization, says Iran is planning to restart activities at the Arak heavy water nuclear reactor -- a move that is not permitted under Tehran’s 2015 nuclear deal with world powers.
Iran’s ISNA news agency quoted Salehi as making the remarks in a meeting with lawmakers in Tehran on July 28.
Heavy water can be employed in reactors to produce plutonium, a fuel used in nuclear weapons.
According to Iranian state TV, Salehi also said that the country has enriched a total of 24,000 kilograms of uranium since 2015 – far beyond the 300 kilogram stockpile limit of the nuclear deal.
In recent weeks, Iran announced that it had exceeded the treaty’s limit on its stockpile of low-enriched uranium. But it had not said by how much.
The treaty allows Tehran to enrich uranium as long as it exports it, rather than stockpiles it in Iran.
Iran has been exporting some of its enriched uranium to Russia in recent years.
Iran in May announced that it would breach the limits allowed under the 2015 nuclear accord in response to the U.S. withdrawal from the deal and the reimposition of U.S. sanctions against Iran.
Meanwhile, Iran's Deputy Foreign Minister Abbas Araqchi met with representatives from Britain, France, Germany, Russia, and China to discuss how to salvage the 2015 nuclear deal.
"The atmosphere was constructive. Discussions were good. I cannot say that we resolved everything. I can say there are lots of commitments," Araqchi told Reuters following the July 28 meeting in Vienna with the remaining parties to the nuclear agreement.
The meeting was called in response to an escalation in tensions between Iran, the United States, and its allies that included confrontations at sea and Tehran's breaches of the accord, which initially included the United States.
Under the pact, Tehran promised to greatly limit its nuclear program in exchange for sanctions relief, but U.S. President Donald Trump pulled out of the deal last year and reimposed crippling sanctions on Iran.
France, Germany, and Britain have tried to salvage the deal and proposed a complicated financial barter system designed to provide some economic relief to Tehran.
However, Iranian officials have complained that the remaining parties to the deal failed to mitigate the effects of the U.S. sanctions on Iran's oil and banking industries.
Iran earlier this month surpassed the uranium stockpile and enrichment limits set out in the 2015 accord, saying it no longer feels bound by the pact.
Russia’s ambassador to international organizations in Vienna, Mikhail Ulyanov, tweeted that the Vienna talks "made it possible to discuss at length the situation around the implementation of this agreement."
"It is obvious that US sanctions negatively affect implementation of the 'nuclear deal.' However all participants are fully committed to it," Ulyanov wrote.