Europe and Japan moved ahead on Tuesday in planning for punitive cuts in oil imports from Iran.
The European Union brought forward a ministerial meeting that is likely to match new U.S. measures to hamper Iran's oil exports.
Japan took precautions in case it joins an international embargo on buying Iranian crude by asking other Gulf countries to help it make up any shortfall.
In Brussels, the European Union said it brought forward by a week, to January 23, a meeting at which foreign ministers from the bloc, rivaling China as Iran's biggest customer for crude, are expected to confirm an embargo on oil purchases.
The 27 EU governments are still debating how quickly some of their oil-dependent economies can afford to do without a key supplier.
Though officially a mere administrative shift to avoid a diary clash with a meeting of EU leaders on January. 30, bringing the foreign ministers' meeting forward could increase the pace of implementation of sanctions, following U.S. President Barack Obama's move on New Year's Eve to stop payments to Iran for oil.