Moscow ? Belarus stepped up its dispute about oil duties with Russia, announcing that it has started a customs case against Russia’s pipeline operator, the Belarusian state news agency reported.

Russia’s trade ministry in turn indicated Saturday it could take retaliatory measures against Belarus.

Belarus this week announced it would charge an import duty of $45 per ton of Russian oil shipped to Western Europe in pipelines that cross Belarus. The move followed Russia’s imposition of an export duty of $180 a ton on oil sold to Belarus.

The dispute so far has not affected Russian oil shipments to Europe.

Russia has called the Belarusian duty a violation of a bilateral trade agreement and out of line with international practice.