Beijing voiced "strong dissatisfaction" on Thursday after the United States announced sanctions on Chinese companies for buying Iranian oil.
China, which is embroiled in a trade war as well as myriad other disputes with Washington, is believed to be the biggest foreign buyer of Iranian oil.
Speaking to a pressure group opposed to the Iranian regime on the sidelines of the United Nations, US Secretary of State Mike Pompeo said Wednesday the actions were in response to violations of unilateral US sanctions.
He said sanctions were being placed both on the companies and on their chief executives.
"China expresses strong dissatisfaction and resolute opposition to the sanctions imposed by the United States on Chinese enterprises and individuals," foreign ministry spokesman Geng Shuang said at a regular press briefing on Thursday.
"Despite the legitimate rights and interests of all parties, the United States wielded a wanton stick of sanctions, which is a gross violation of the basic norms of international relations," Mr Geng said.