The United States blacklisted on Friday, May 30 eight companies in Iran's petrochemical industry, sending a warning to the Islamic Republic's global customers as Washington strives to cut off funds to the country's nuclear program, Reuters said.

Petrochemical companies owned or controlled by the Iranian government that are on the Treasury Department list include Bandar Imam Petrochemical Co, Bou Ali Sina Petrochemical Co and Mobin Petrochemical Co.

This was the first time Washington sanctioned the petrochemical industry, which an administration official said was the largest source of foreign earnings for Iran's nuclear program after oil sales.

In a related action, the U.S. State Department imposed sanctions on Niksima Food and Beverage JLT, a frozen yogurt company based in the UAE, for "knowingly engaging" in a transaction for the purchase of petrochemical products from Iran. It also sanctioned Jam, an Iranian manufacturer and seller of petrochemicals. The sanctions effectively cut them off from the U.S. financial system.

Western powers believe Iran is trying to develop the ability to make nuclear weapons. Tehran has said the program is purely for generating power and for medical devices.

Sanctions imposed by the United States and European Union halved Iran's oil exports last year, depriving the government of billions of dollars in revenue, increasing already high inflation and pushing down the value of its currency, the rial.