Beijing issued a formal diplomatic protest on Sunday after the Trump administration's latest round of secondary sanctions targeting Chinese oil refineries and shipping companies took effect, escalating tensions between Washington and Beijing over Iran energy trade. China's Ministry of Foreign Affairs summoned the US chargé d'affaires in Beijing, calling the sanctions 'a gross violation of international law and an act of unilateral economic coercion.'

The US Treasury Department announced the measures on Thursday, designating a China-based refinery and approximately 40 shipping entities for handling Iranian crude in defiance of existing sanctions. The move is part of the Trump administration's 'maximum pressure' campaign against Tehran, which also includes the ongoing diplomatic track being pursued through envoys Steve Witkoff and Jared Kushner in Pakistan.

China's commerce ministry separately announced it was initiating a review of American firms operating in China under its 'unreliable entity' framework, a mechanism Beijing has previously used to signal readiness for economic retaliation. Chinese state media described the US measures as an attempt to 'strangle legitimate energy cooperation between sovereign nations.'

Analysts noted the timing is particularly fraught given the delicate US-Iran negotiating process. Some observers warned that Chinese retaliation could complicate Tehran's incentive to reach a nuclear deal, since Beijing provides a key economic lifeline that reduces Iran's pressure to compromise. 'Washington is simultaneously squeezing Iran through sanctions and courting it through diplomacy — Beijing just made that contradiction visible,' said one regional energy analyst.

Oil markets responded cautiously on Sunday, with Brent crude rising modestly as traders assessed whether the sanctions would meaningfully reduce Iranian export volumes or simply redirect trade through less visible channels. Shipping industry sources indicated several of the designated vessels had already shifted flag registrations in recent weeks, suggesting advance awareness of the impending designations.