Aug. 28 (UPI) -- Germany, the United Kingdom and France sent a letter Thursday to the United Nations Security Council saying they are starting the 30-day process of "snapback" of sanctions against Iran.

The snapback is used to re-impose sanctions on Iran in the event of "significant non-performance" of treaty commitments. The sanctions were suspended under the 2015 Joint Comprehensive Plan of Action nuclear deal.

The three countries, known as the E3, created an Aug. 31 deadline to make meaningful progress toward a nuclear deal, such as by renewing cooperation with the International Atomic Energy Agency and resuming negotiations with the United States.

"Today, Iran's non-compliance with the JCPOA is clear and deliberate, and sites of major proliferation concern in Iran are outside of IAEA monitoring," an E3 joint statement said. "Iran has no civilian justification for its high enriched uranium stockpile -- now over nine significant quantities -- which is also unaccounted for by the IAEA. Its nuclear program, therefore, remains a clear threat to international peace and security."

U.S. Secretary of State Marco Rubio announced Thursday that the United States "welcomes the initiation of snapback."