Washington has increasingly targeted Chinese companies over the export of Iran's petrochemicals as the prospects of reviving the nuclear pact have dimmed. Indirect talks on the accord, formally known as the Joint Comprehensive Plan of Action (JCPOA), have broken down.

"So long as Iran refuses a mutual return to full implementation of the Joint Comprehensive Plan of Action, the United States will continue to enforce its sanctions on the sale of Iranian petroleum and petrochemical products," the Treasury's Under Secretary for Terrorism and Financial Intelligence Brian Nelson said in a statement.

The Iranian mission to the United Nations in New York did not immediately respond to a request for comment.

U.S. Secretary of State Antony Blinken said in a separate statement that the State Department designated two China-based companies, Zhonggu Storage and Transportation Co Ltd and WS Shipping Co Ltd.

Blinken accused Zhonggu Storage and Transportation Co Ltd of operating a commercial crude oil storage facility for Iranian petroleum and WS Shipping Co Ltd of being a ship manager for a vessel that has transported Iranian petroleum products.

Reuters could not immediately reach the two companies for comment.

The U.S. Treasury Department also slapped sanctions on a network of companies involved in what it said was the sale of hundreds of millions of dollars worth of Iranian petrochemical and petroleum products to South and East Asia.

The action targeted Iranian brokers and front companies in the United Arab Emirates, Hong Kong and India, the Treasury said.

Washington warned that it would continue to accelerate enforcement of sanctions on Iran's petroleum and petrochemical sales so long as Tehran continues to accelerate its nuclear program.

CRIPPLED ECONOMY

The 2015 nuclear agreement limited Iran’s uranium enrichment activity to make it harder for Tehran to develop nuclear arms, in return for lifting international sanctions.

But then-U.S. President Donald Trump ditched the deal in 2018, saying it did not do enough to curb Iran’s nuclear activities, ballistic missile program and regional influence, and reimposed sanctions that have crippled Iran’s economy.

"These enforcement actions will continue on a regular basis, with an aim to severely restrict Iran’s oil and petrochemical exports," Blinken said.

Anyone involved in such sales and transactions should stop immediately if they wish to avoid being subjected to U.S. sanctions, he said.

As part of Thursday's action, the Treasury targeted several companies it accused of dealing with Hong Kong-based Triliance Petrochemical Co Ltd, which has previously been sanctioned by the United States.

It said India-based petrochemical company Tibalaji Petrochem Private Limited purchased millions of dollars worth of Triliance-brokered products for onward shipment to China.

The Treasury also accused UAE-based Clara Shipping LLC of being paid millions of dollars by Triliance - through front companies - in freight charges for the shipment of Iranian petrochemical and petroleum products to East Asia.

Also designated over dealings with Triliance was Iran-based Iran Chemical Industries Investment Company and Middle East Kimiya Pars Co, Hong Kong-based Sierra Vista Trading Limited, and UAE-based Virgo Marine.

Hong Kong-based Sophychem HK Limited and ML Holding Group Limited were designated for dealings with U.S.-designated Persian Gulf Petrochemical Industries Commercial Company, including the purchase of Iranian petrochemicals for shipment to China and Singapore.

Reuters was unable to immediately reach the companies for comment.