A threat from Iran, and its nuclear capabilities, has a number of countries responding.
Iran says it has exceeded its agreed-to limit on enriched uranium stockpiles.
The announcement marks the first time Tehran has acknowledged breaching its 2015 nuclear agreement.
The claim has now been confirmed by the United Nations.
A spokesman for the U.N. Secretary General urged Tehran to try to salvage the deal.
Iraeli Prime Minister Benjamin Netanyahu said Iran had taken what he called a "significant step toward developing nuclear weapons."
Netanyahu urged the European Union to reimpose sanctions.
Monday, the White House issued a statement that said Tehran was violating the terms of the nuclear agreement, "even before the deal's existence."
Iran says that it will further enrich its uranium starting next week if the European Union fails to offer it a new nuclear deal.