WASHINGTON, Dec 18 (Reuters) - The United States imposed sanctions on Thursday on 29 vessels and their management firms as Washington targeted Tehran's "shadow fleet", which it says exports Iranian petroleum and petroleum products.

The targeted vessels and companies ⁠have transported hundreds of millions of dollars of the products through ⁠deceptive shipping practices, the U.S. Treasury said.

The shadow fleet refers to ships that carry ‍oil that is under sanctions. They are typically old, their ownership opaque and they sail without the top-tier insurance cover needed to meet international standards for oil majors and many ports.

Treasury will "continue to deprive the regime of the petroleum revenue it uses to fund its military and weapons programs," John Hurley, the department's undersecretary for terrorism and financial intelligence, said in a release.

Iran's mission to the United Nations did not immediately respond to a request for comment.

The U.S. says it imposes sanctions on Iran over Tehran's nuclear program and its support of militant proxies ;across the Middle East. Iran says its ‍nuclear work is for civil purposes.

Tensions between Tehran and Washington heightened after the two ‍countries engaged in five rounds of indirect nuclear negotiations that ended with a 12-day air war in June in which Israel and the U.S. bombed Iranian nuclear sites.

Thursday's action also targets Egyptian businessman Hatem Elsaid Farid Ibrahim Sakr, whose companies are ⁠associated with seven of the vessels cited, as well as multiple shipping companies.

The U.S. ‍this month took ​further action on a tanker carrying Venezuelan oil that had originally been sanctioned by Washington for transporting Iranian oil.

The U.S. seized a tanker known as Skipper on December 10 off the coast of Venezuela that had been carrying ;crude from the South American country, a move that sharply ⁠escalated ‍tensions between Washington and Caracas.

The administration of former President Joe Biden imposed sanctions on the tanker in ‍2022 for what it says was involvement in trading Iranian oil when ;the ship was called ‍the Adisa.

(Reporting by Timothy ​Gardner and Doina Chiacu; additional reporting by Michelle Nichols in New York, Editing by Caitlin Webber and Nia Williams)