WASHINGTON -- The U.S. Treasury Department on July 18 imposed additional sanctions on Iran that target its nuclear-enrichment program.

They are the first restrictive measures since Tehran said earlier this month that it would increase enriched uranium levels to above those allowed under the terms of a 2015 nuclear accord.

The blacklist includes five people and an international group of companies in Iran, Belgium, and China that acted as a supply network for Iran’s nuclear program.

The individuals and entities are subject to asset freezes within the United States and will be denied access to the U.S. financial system as well as listed as “weapons of mass destruction proliferators,” U.S. Secretary of State Mike Pompeo said in a statement.

"Iran cannot claim benign intent on the world stage while it purchases and stockpiles products for centrifuges," Treasury Secretary Steven Mnuchin in a statement.

Tehran had initially promised to greatly limit its nuclear program in exchange for economic benefits based on a 2015 accord with six world powers, including the United States.

Last year, U.S. President Donald Trump pulled out of the deal and reimposed economically crippling sanctions in many sectors, including the crucial oil and financial industries.

France, Germany, and Britain -- three of the six remaining accord signatories -- have tried to salvage the deal and have proposed a complicated financial barter system designed to provide some economic relief to Tehran.

Iran says it no longer feels bound by the accord and on July 1 said it had amassed more than the permitted amount of low-enriched uranium.