Iran is injecting uranium gas into advanced centrifuges in a further breach of its 2015 nuclear deal with world powers, officials said Saturday.
The country's atomic energy spokesman warned that "Europeans should know that there is not much time left" to save the 2015 deal.
Iran has already gone beyond the stockpile and enrichment level limits set by the deal.
Behrouz Kamalvandi of the Atomic Energy Organization of Iran made the remarks Saturday in a news conference carried on live television. He spoke from a podium as centrifuges stood next to him.
He that Iran had the ability to go beyond 20 percent enrichment of uranium, which analysts say is just a short technical step away from weapons-grade level 90 percent enrichment.
"All these steps are reversible if the other side fulfils its promises," Kamalvandi said.
Kamalvandi warned several times in his comments that Iran was rapidly approaching a point that would mean a full withdrawal from the deal.
"Our stockpile is quickly increasing, we hope they will come to their senses," he said.
However, he added that Iran will continue to allow U.N. inspectors to access nuclear sites in the country.
Enriched uranium is used in energy production, although stockpiling uranium is also a necessary step to building nuclear weapons, which Iran has denied doing.
European powers have called on Iran to pull back from the slippery slope that could undo the accord completely.
It began falling apart last year after President Donald Trump withdrew the United States from the deal, followed by escalated U.S. sanctions that have sent Iran's economy into freefall.
Tensions between the two countries have risen in recent months that have seen mysterious attacks on oil tankers near the Strait of Hormuz, Iran shooting down a U.S. military surveillance drone and other incidents across the wider Middle East.
Also on Saturday, satellite images showed a once-detained Iranian oil tanker pursued by the U.S. appears to be off the coast of Syria, where Tehran reportedly promised the vessel would not go when authorities in Gibraltar agreed to release it several weeks ago.
Iranian Foreign Minister Mohammad Javad Zarif has repeatedly called the sanctions "economic terrorism." Iran views its scaling back on the nuclear accord as "maximum pressure" in the face of the U.S. policy by the same name.
Zarif argued Friday that U.S. sanctions "target ordinary Iranian citizens, the civilians." He insisted that the Iranian nuclear program was for peaceful purposes.
Zarif made a surprise visit to the G-7 gathering of world leaders in Biarritz last month, prompting renewed hope for talks between Tehran and Washington brokered by the French government.
But Iranian president Hassan Rouhani later reiteratedthat talks would only be possible if the U.S. first lifts sanctions.
Defense Secretary Mark Esper said Friday that it appeared Iran was inching toward a place where talks could be held, days after Trump left the door open to a possible meeting with Rouhani.
The two leaders are both due to attend the U.N. General Assembly in New York later this month.