The Iranian government has reported that the 300kg limit on its stockpile of enriched uranium laid out in the 2015 nuclear agreement has been exceeded.
US President Donald Trump pulled America out of the deal a year ago.
"Based on what I have been told," explained Foreign Minister Javad Zarif, "Iran has exceeded the 300kg limit in accordance with its plan." He pointed out that the government had announced this previously. "We have clearly said what we will do and we will act accordingly. We deem it as part of our rights under the  Joint Comprehensive Plan of Action."
The International Atomic Energy Agency (IAEA) has yet to verify the claim, and is sending inspectors to file a report.
If the claim is verified by the IAEA and Iran has indeed breached the terms of the nuclear deal, it can expect multilateral sanctions to be imposed, with European nations saying that there would be consequences.
The Iranian announcement comes as tensions rise in the Gulf region, with the US accusing Tehran of attacking oil tankers in regional waters. Tensions were further heightened when Iran shot down a US military drone last week, claiming that it was in Iranian airspace.
Trump and Zarif have traded verbal blows on Twitter, which has seen the American leader threaten Iran with "obliteration" in response to President Hassan Rouhani's statement that the White House is afflicted with "mental retardation". Zarif responded to the threat by implying that if the US starts a war with the Iranians, it "will not be the one to end it".