Iran has exceeded its agreed limit of enriched uranium stockpiles, state media quoted Foreign Minister Mohammad Javad Zarif as saying on Monday.
IRNA news agency, an Iranian state-run outlet, said Zarif confirmed the breach in response to a reporter asking if the country had surpassed its 300kg limit of uranium enriched up to 3.67%.
Exceeding this limit would violate an international nuclear treaty signed in 2015, and would mark the first major reaction to the US pulling out of the deal last year.
Enriched uranium can be used to create nuclear-grade weapons - but the limits stipulated under the deal ensured that such weapons would never be manufactured in Iran.
Tensions have been high for months between Iran, the US and the deal's remaining signatories, including the UK, France, Germany, China and Russia.
In May, Iran warned of ceasing "some commitments" to the treaty in response to the US pulling out and reapplying crippling economic sanctions on the country.
It gave the remaining signatories a time limit of July 7 to renegotiate a new deal, or see Iran resuming its manufacturing of enriched uranium beyond the 3.67% limit.
More recently, Iran shot down a US military surveillance drone and several unexplained attacks on oil tankers in the Persian Gulf have all heightened diplomatic uncertainty.
WATCH: Euronews journalist, Masoud Imani Kalesar says that whilst the 300kg cap has been exceeded, the amount won't allow them to build a nuclear weapon - but it does serve as a warning.