Iran has followed through on its threats to surpass the limit on its stockpile of low-enriched uranium that was set by the 2015 nuclear deal. The BBC reports Iran’s foreign minister confirmed the 300-kilogram (or 600-pound) cap had been exceeded Monday morning—the breach of the limit is in direct response to the reinstatement of U.S. sanctions. Enriched uranium can be used to make reactor fuel and potentially a nuclear weapon. The breach hasn’t yet been confirmed by the International Atomic Energy Agency, but the group said it would be investigating the claims and filing a report. The apparent unraveling of the nuclear agreement comes as tensions flare between Iran and the U.S. after Iran shot down an American drone last month.