TEHERAN/WASHINGTON－Iran announced on Monday a more than tenfold increase in enriched uranium production, thus further stepping back from commitments it made under a landmark 2015 nuclear deal abandoned by the United States.

The Islamic republic has also developed two advanced centrifuges, one of which is undergoing testing, said Ali Akbar Salehi, the head of the Atomic Energy Organization of Iran.

Enriched uranium production has reached five kilograms 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.

Teheran 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.

Teheran 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, Russia and the European Union－fail to help it circumvent US sanctions.

After the latest announcement, the EU warned that its support for the nuclear deal depends on Teheran 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-kg 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 Sept 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".

Teheran denies a US claim that it aims to develop a nuclear bomb, saying its enrichment is only to generate energy for civilian uses.

Mass demonstrations

The announcement also came as Iranians held demonstrations nationwide to mark the 40th anniversary of the seizure of the US embassy in Teheran, while the Iranian officials continued to defy the escalating US pressures.

In Teheran, demonstrators gathered outside the former US embassy, now called a "den of espionage", carrying placards condemning US policies against Iran.

The embassy was stormed by Iranian students on Nov 4, 1979, and its staff were held hostage for 444 days. The US broke off diplomatic relations with Iran in 1980 and the ties between the two countries have since remained severed.

On Monday, Iranian President Hassan Rouhani said: "The US government has realized that its pressures, including those of sanctions, against the Islamic republic have been a failed policy."

Washington marked the anniversary by slapping sanctions on nine aides to Iran's supreme leader Ayatollah Ali Khamenei.

"Today the Treasury Department is targeting the unelected officials who surround Iran's supreme leader, Ayatollah Khamenei, and implement his destabilizing policies," said US Treasury Secretary Steven Mnuchin in a statement.

The action, which targets Khamenei's appointees in the Office of the Supreme Leader, the Expediency Council, the Armed Forces General Staff, and the Judiciary, seeks to block funds from flowing to a network of Khamenei's military and foreign affairs advisers, the statement said.

Separately, the US State Department announced a new reward of up to $20 million for information that leads to the location, recovery and return of Robert Levinson, a former FBI agent who was last seen in Iran in 2007.

Agencies-Xinhua