Iran said on Saturday that it is now enriching uranium to five percent, after stepping back from its commitments under the troubled 2015 accord with significant powers.
The deal four years ago set a 3.67 percent limit for uranium enrichment, but Tehran announced it would no longer respect it after the United States unilaterally abandoned the agreement last year and reimposed crippling sanctions.
"Based on our needs and what we have been ordered, we are currently producing five percent," said Behrouz Kamalvandi, a spokesman for the Atomic Energy Organisation of Iran.
At a news conference, he said that Iran has the "capacity to produce five percent, 20 percent, 60 percent, or any percentage" of enriched uranium, a claim often repeated by Tehran.
Uranium enrichment is a sensitive process that produces fuel for nuclear power plants but also, in highly extended form, the fissile core for a warhead.
The current five percent-level exceeds the limit set by the accord but is less than the 20 percent Iran had previously operated and far less than the 90 percent-level required for a warhead.
In its fourth step away from the agreement, Iran resumed enrichment at the Fordow plant south of Tehran on Thursday, with engineers feeding uranium hexafluoride gas (UF6) into the plant's mothballed enrichment centrifuges.
Iran was already enriching uranium at another plant in Natanz, where a United Nations inspector was denied access to the site last week.
Kamalvandi said that "legally speaking" the Iranian government had done nothing wrong in blocking the female inspector from its facility.
Iran alleged the inspector tested positive for suspected traces of explosive nitrates but the UN's nuclear watchdog disputed the claim.
It marked the first known instance of Iran blocking an inspector amid tensions over its collapsing nuclear deal with world powers.
Kamalvandi said Iran had not imposed any restriction on inspections, but warned against using them for "sabotage and leaking information".
Tehran says it would reverse the measures it has taken if the remaining parties to the deal - the United Kingdom, China, France, Germany and Russia - find a way to get around US sanctions.
On July 1, Iran said it had increased its stockpile of enriched uranium to beyond a 300-kilogramme limit set by the deal, and a week later, it announced it had exceeded the enrichment cap.
The third move had it firing up advanced centrifuges on September 7 to enrich uranium faster and to higher levels.