The US has taken sanctions against three oil companies that traded with Iran.
One of them was China's state-run Zhuhai Zhenrong Corp, which the US said was Iran's largest supplier of refined petroleum products.
The other two were Singapore's Kuo Oil and FAL Oil, an energy trade based in the United Arab Emirates.
The State Department said the sanctions were part of efforts to persuade Iran to rein in its nuclear ambitions.
The sanctions came days after US Treasury Secretary Tim Geithner visited China to urge its government to do more to put pressure on Iran.
The sanctions will prevent the three companies from receiving US export licences, US Export Import Bank financing or any loans over $10m from US financial institutions.
Analysts said the sanctions against Zhuhai Zhenrong were largely symbolic, given that the company would be unlikely to do much business in the US.
It may be seen as more of a threat to larger Chinese energy companies, which have made large investments in the US energy sector.
"It's a good shot across the bow and signals the US is serious about vigorous sanctions enforcement," said Mark Dubowitz, executive director of the Foundation for Defense of Democracies.
"This could be the beginning of a cascade of more sanctions on Chinese companies if China doesn't curtail its Iranian trade."