President Hassan Rouhani's threat, combined with Iran surpassing the stockpile limits of the 2015 atomic accord, could narrow the estimated one-year window it would need to produce enough material for a nuclear weapon, something Iran denies it wants but the deal sought to prevent.
But as tensions rise a year after President Donald Trump unilaterally withdrew America from the deal, it looks unlikely that Europe can offer Iran a way to sell its oil on the global market despite U.S. sanctions.
All this comes as the U.S. has rushed an aircraft carrier, B-52 bombers and F-22 fighters to the region and Iran recently shot down a U.S. military surveillance drone. "Be careful with the threats, Iran. They can come back to bite you like nobody has been bitten before!" Trump tweeted in response to Rouhani's warning.
On Wednesday, Iran also marked the anniversary of the U.S. Navy shooting down an Iranian passenger jet in 1988, a mistake that killed 290 people and shows the danger of miscalculation in the current crisis.
"The Trump administration is pushing the center of Iranian politics to the right at the determent of the Iranian people and the entire region," said Ali Vaez, an Iran analyst for the International Crisis Group. "Rouhani is clearly at the end of his rope and has no choice other than green lighting further escalation."
Rouhani, still viewed inside Iran as a relatively moderate cleric in the country's Shiite theocracy, has taken an increasingly hard-line tone in his remarks to the West. Particularly, he and others in his administration target European signatories to the nuclear deal for not doing enough to ease restrictions on Iran's oil and financial sectors.
That continued Wednesday in a televised address to his Cabinet. His remarks seemed to signal that Europe has yet to offer Iran anything to alleviate the pain of the renewed U.S. sanctions targeting its oil industry and top officials.
The deal saw Iran agree to limit its enrichment of uranium to 3.67%, which is enough for nuclear power plants but far below the 90% needed for weapons. It also limited its stockpile of enriched uranium to 300 kilograms (661 pounds). In exchange, Iran saw crippling economic sanctions lifted.
But after Trump withdrew from the deal, those sanctions and even more-stringent newer ones took effect. On Monday, both Iran and the U.N.'s nuclear watchdog agency confirmed that Tehran had breached that stockpile limit.
Rouhani some two months earlier set the Sunday deadline that Iran would increase its enrichment of uranium. Wednesday's remarks underlined that.
"From July 7 onward, the level of our enrichment will not be at 3.67% anymore," Rouhani said. "We will put aside this commitment as much as we want to and to any level we think is necessary and we need."
However, Rouhani's remarks, while strident, seemed to still insist last-minute diplomacy could be possible.
"Our advice to Europe and the United States is to go back to logic and to the negotiating table," he said. "Go back to understanding, to respecting the law and resolutions of the U.N. Security Council. Under those conditions, all of us can abide by the nuclear deal."
There was no immediate reaction in Europe, where the EU just the day before finalized nominations to take over the bloc's top posts.
On Tuesday, European powers separately issued a statement on Iran breaking through its stockpile limit, calling on Tehran "to reverse this step and to refrain from further measures that undermine the nuclear deal."
Vaez, the Iran analyst, said the current state of the deal forced Rouhani to shift right, while also highlighting the limitations faced by Europe.
"It is a pity that despite its goodwill and efforts, Europe fell short of preserving an agreement that incarnates European belief in multilateralism," he said.
The heightened tensions between the U.S. and Iran have seen a series of incidents spiral across the wider Persian Gulf. Mysterious attacks have struck oil tankers near the Strait of Hormuz, which the U.S. and Israel blame on Iran, although Tehran denies involvement.
Yemen's Iranian-backed Houthi rebels have launched a series of bomb-laden drone attacks on Saudi Arabia. Iran also shot down an over $100 million U.S. military surveillance drone on June 20, nearly sparking a retaliatory American strike.
Iranian state TV reported that the powerful Imam Reza Foundation, a religious body that manages vast endowments and businesses across Iran, awarded medals to those who shot down the U.S. drone.
Meanwhile, relatives of those killed the 1988 downing of Iran Air Flight 655 by the U.S. Navy marked the day by visiting the site in the Strait of Hormuz where its debris fell.
Iranian TV showed video of the mourners as armed Iranian Revolutionary Guard fast boats patrolled around them. They tossed gladiolas and roses into the strait from the boat and by helicopter as some wept.
"Thirty years of being an orphan!" one woman screamed. Others chanted: "Death to America!"
Just after dawn on July 3, 1988, the USS Vincennes chased Iranian speedboats into Iranian territorial waters after they allegedly shot at an American helicopter. It began firing at the Iranian vessels there.
The Vincennes then mistook Iran Air flight 655, which had taken off from Bandar Abbas, Iran, heading for Dubai in the United Arab Emirates, for an Iranian fighter jet. It fired missiles, killing all 290 people on board.
The U.S. later would give USS Vincennes Capt. William C. Rogers the country's Legion of Merit award, further angering Iran.
The downing of the flight remains one of the moments the Iranian government points to in its decades-long distrust of America. They rank it alongside the 1953 CIA-backed coup that toppled Iran's elected prime minister and secured Shah Mohammad Reza Pahlavi's absolute power until he abdicated the throne before the 1979 Islamic Revolution.
Foreign Minister Mohammad Javad Zarif marked the holiday by writing on Twitter: "US aggression against Iran did not begin with @realdonaldtrump."