A classified International Atomic Energy Agency report found Iran, since February, produced 300 pounds of uranium enriched to 60%, a step away from weapons-grade.

The United States has sent its first nuclear deal proposal to Iran since negotiations began in April, a move that comes after a U.N. nuclear watchdog report indicated the Middle Eastern country significantly increased its uranium enrichment over a three-month span.

The U.N. atomic agency reports that Iran hasn’t cooperated with a nuclear probe, raising the prospect of a snapback of sanctions on Tehran.