Iran has never agreed to entirely stop enriching uranium, a process needed to create nuclear fuel.
Iran Supreme Leader Ayatollah Khamenei said in March 2021 that Iran’s “definite policy” is that the nation will only recommit to the Joint Comprehensive Plan of Action, the 2015 nuclear deal, if the U.S. lifts sanctions against Iran. In the 2015 agreement Iran agreed to a 3.67% limit on uranium-235 enrichment. In May 2021, Iran began enriching uranium up to 63% following an explosion at its Natanz enrichment plant. Lower levels of enriched uranium can be used to fuel nuclear power plants. Uranium enriched beyond 90% can be used to make nuclear weapons.
The U.S. withdrew from the 2015 agreement in May 2018, reimposing all sanctions on Iran that the deal had previously lifted. Iran then began violating the agreement’s terms.