U.S. Secretary of State Hillary Clinton imposed sanctions on Zhuhai Zhenrong Co, based in China, Kuo Oil, based in Singapore, and FAL Oil Co. Ltd, based in the United Arab Emirates.
"Under the sanctions imposed today, all three companies are barred from receiving U.S. export licenses, U.S. Export Import Bank financing, and loans [of] over $10 million from U.S. financial institutions," the State Department said in a statement.
The department identified the Chinese company as the largest supplier of refined petroleum product to Iran. U.S. Treasury Secretary Timothy Geithner this week was unsuccessful in convincing Beijing to back away from the Iranian energy sector, though the State Department stressed the sanctions targeted individual companies and not their governments or countries.
Increased sanction pressure on Iran caused the country's military to threaten to close key oil shipping lanes in the Strait of Hormuz. This, in turn, caused oil prices to rise.
Western allies believe Iran is working to develop the technology needed to build a nuclear weapon. Iran, however, insists its intentions are peaceful.
"The United States is working with international partners to maintain pressure on the government of Iran to comply with its international nuclear obligations," the State Department said.