The Treasury Department said it placed sanctions on Iran's Sambouk Shipping company as an active participant in ship-to-ship transfers of Iranian oil in the Persian Gulf. This method was employed to try to obscure the origin of the oil, the department said.
"As Iran becomes increasingly isolated from the international financial system and energy markets, it is turning increasingly to convoluted schemes and shady actors to maintain its access to the global financial system," Undersecretary for Terrorism and Financial Intelligence David Cohen said in a statement.
Sanctions imposed on Iran's energy sector are meant to rob it of revenue to finance its nuclear program. U.N. inspectors said they have concerns about the intent of the program, though Iran says it's for peaceful purposes.
The level of Iranian crude oil exports has been in steady decline, though some countries can get waivers from the U.S. government if they show "significant" reductions in crude oil purchases.
"As long as Iran tries to evade our sanctions, we will continue to expose their deceptive maneuvers," Cohen said.