Iran says it has further scaled back its commitments under the 2015 nuclear deal with world powers, saying it is now operating twice as many advanced centrifuges banned by the agreement.
The country now has a prototype centrifuge that works 50 times faster than those allowed under the deal, the head of Iran's Atomic Energy Organization, Ali Akbar Salehi, said on November 4, adding that the moves would show Iran's "capacity and determination."
The announcements come as the country commemorates the 40th anniversary of the 1979 student takeover of the U.S. Embassy in Tehran and the subsequent 444-day hostage crisis -- which the White House called a "brazen act."
U.S. President Donald Trump last year withdrew the United States from the 2015 nuclear accord between Tehran, and has since reimposed and expanded punishing sanctions as part of a stated campaign of "maximum pressure" against Iran.
Meanwhile, Tehran has gradually reduced some of its commitments in the deal, under which it had curbed its nuclear program in exchange for sanctions relief.
It had warned previously that it would announce new steps in November.
Iranian officials complain that the remaining parties to the deal have failed to mitigate the effects of the U.S. sanctions.
Earlier on November 4, Iranian state media reported government-sponsored rallies in nearly 1,000 cities and towns across the country for annual commemorations marking the takeover of the U.S. Embassy in Tehran.
On November 4, 1979, Iranian militant students stormed the diplomatic mission and took 52 Americans hostage for 444 days after Washington refused to hand over Iran's toppled shah, Mohammad Reza Pahlavi, for trial in Iran.
PHOTO GALLERY: Looking Back At The U.S.-Iran Hostage Crisis (click to enlarge)
444 Days: Looking Back At The U.S.-Iran Hostage Crisis
The two countries have had no diplomatic relations since then.
"Today, we honor the victims of this brazen act," a White House spokeswoman said in a statement, adding: "The Iranian regime continues to target innocent civilians for use as pawns in its failed foreign relations."
"Until Iran changes this and its other hostile behavior, we will continue to impose crippling sanctions," said spokeswoman Stephanie Grisham.
In Tehran, state television showed crowds packing the streets around the former embassy dubbed the "den of spies" after the 1979 Islamic Revolution. News agencies posted images of protesters setting the U.S. flag on fire.
Participants were chanting slogans against the United States, including "Death to America," and Israel, according to the hard-line Fars news agency.
"Our fight with America is over our independence, over not submitting to bullying, over values, beliefs, and our religion," army chief Major General Abdolrahim Musavi said in a speech at the rally.
The United States "will continue its hostilities...unless it is crushed," Musavi said in remarks carried by state-run television.
Iranian Supreme Leader Ayatollah Ali Khamenei on November 3 renewed a ban on talks with the United States, describing the two countries as implacable foes.
"Those who believe that negotiations with the enemy will solve our problems are 100 percent wrong," Khamenei was quoted as saying by domestic media.
Trump wants to force Iran to renegotiate the 2015 nuclear accord, arguing that the terms were not tough enough to prevent the country from developing nuclear weapons, agree curbs to its ballistic-missile program, and end its "malign" activities in the Middle East.
Iran has denied it supports insurgent activity and said its nuclear program was strictly for civilian energy purposes. Iranian officials have also ruled out any negotiations on its missile program.