The US has imposed sanctions on an independent "teapot" refinery in China for buying billions of dollars worth of Iranian oil. The Treasury Department targeted Hengli Petrochemical (Dalian) Refinery Co, one of Iran's largest customers of crude oil and petroleum products. The sanctions also imposed on about 40 shipping companies and vessels associated with Iran's shadow fleet. This comes as Washington and Tehran struggle to restart peace talks. The independent refineries are typically immune to the full effect of U.S. sanctions as they have limited exposure to the US financial system.