The U.S. measure adds tariffs to exports from countries that continue energy transactions with Russia. As a form of secondary sanction aimed at Russian fiscal revenue, it differs from earlier measures by making trading partners in general the object of pressure.

China's commerce ministry replied to questions by saying it opposes unilateral measures without a basis in international law and will take necessary steps to protect the legitimate rights of its companies. Beijing has maintained that diversifying energy sources is a commercial judgment for its firms.

The U.S. side argues that closing workaround routes is necessary for sanctions to bite. Imposing costs on purchasers, it says, is required to sever the flow of energy revenue into war financing.

India, Turkey and other large buyers of Russian crude are also in range. With refining margins, marine insurance and settlement currencies all entangled, how exemptions are drawn in implementation is the central question.

Korea and Taiwan import little Russian energy directly, so the immediate impact is limited. But when crude and spot liquefied natural gas prices move, power generation costs and petrochemical feedstock bills follow with a lag.