Iran announced Monday a more than tenfold increase in enriched uranium production following a series of steps back from commitments under a 2015 nuclear deal abandoned by the United States.
The Islamic republic has also developed two new advanced centrifuges, one of which is undergoing testing, Ali Akbar Salehi, the head of the Atomic Energy Organisation of Iran, announced.
Enriched uranium production has reached five kilogrammes per day, Salehi told reporters at the Natanz facility in central Iran in remarks broadcast by state television.
That compares with the level of 450 grams two months ago.
Tehran decided in May to suspend certain nuclear commitments, a year after US President Donald Trump withdrew from the deal between world powers and Iran and reimposed sanctions on the country.
Tehran has so far hit back with three packages of countermeasures and threatened to go even further if the remaining partners to the deal -- Britain, China, France, Germany and Russia -- fail to help it circumvent US sanctions.
After the latest announcement, the European Union warned that its support for the nuclear deal depends on Tehran fulfilling its commitments.
"We have continued to urge Iran to reverse such steps without delay and to refrain from other measures that would undermine the nuclear deal," said Maja Kocijancic, spokeswoman for EU diplomatic chief Federica Mogherini.
Although the EU "remained committed" to the accord, "we have also been consistent in saying that our commitment to the nuclear deal depends on full compliance by Iran", she told reporters in Brussels.
On July 1, Iran said it had increased its stockpile of enriched uranium to beyond a 300-kilo maximum set by the deal, and a week later, it announced it had exceeded a 3.67-percent cap on the purity of its uranium stocks.
It fired up advanced centrifuges to boost its enriched uranium stockpiles on September 7.
Salehi said Iranian engineers "have successfully built a prototype of IR-9, which is our newest machine, and also a model of a new machine called IR-s ... all these in two months".
EU deadline over
Iran has removed all of its IR-1 centrifuges -- the sole deal-approved machines -- and is now using advanced models, leading to the sharp increase in enriched uranium production, he added.
"We must thank the enemy for bringing about this opportunity to show the might of the Islamic republic of Iran, especially in the nuclear industry," Salehi said.
"This is while some say (Iran's) nuclear industry was destroyed!" he said, laughing.
Iran will take the fourth step of walking back on the nuclear accord on Tuesday, semi-official news agency ISNA reported without specifying details.
The announcement came as Iranians held mass rallies four decades to the day after revolutionary students stormed the US embassy in the capital and took dozens of American diplomats and staff hostage.
It took a full 444 days for the crisis to end with the release of 52 Americans, but the US broke off diplomatic relations with Iran in 1980 and ties have been frozen ever since.
Monday also marked the end of the 60-day deadline Iran gave to Europe to either provide it with the economic benefits of the nuclear agreement or see even more commitments abandoned.
The European parties to the Vienna deal have repeatedly called on Iran to stay within the accord's framework but their efforts to skirt unilateral US sanctions have so far borne no fruit.
Iran's supreme leader Ayatollah Ali Khamenei called French President Emmanuel Macron's efforts to set up talks between Iran and the US to break the impasse "naive".
Macron's efforts to initiate a phone call between US President Donald Trump and his Iranian counterpart Hassan Rouhani on the sidelines of the UN General Assembly in September ended in failure.
Rouhani stressed he would only hold talks with the US if sanctions were lifted first.