WASHINGTON, Sep 29 (Reuters) - The United States on Thursday (Sep 29) imposed sanctions on companies it accused of involvement in Iran's petrochemical and petroleum trade, including five based in China, pressuring Tehran as it seeks to revive the 2015 Iran nuclear deal.

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 US 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.