BRUSSELS — The European Union is set to extend by six months economic sanctions against Russia, calming fears that Greece’s acrimonious negotiations over its debt crisis might allow Russia to break the unity of the 28-nation bloc in its response to the conflict in Ukraine.

A decision to prolong the sanctions, which expire at the end of July, was made by European ambassadors in Brussels on Wednesday and is expected to be ratified at a meeting of foreign ministers early next week in Luxembourg, diplomats in Brussels said.

Moscow lobbied hard against a renewal of the sanctions, imposed last year in tandem with similar measures by the United States after Russia annexed Crimea in March and then provided support to separatist rebels in eastern Ukraine. Decisions on sanctions require unanimity, so Russia needed to win over only one European Union country to block an extension. But it failed in efforts to secure a blocking vote from any of the countries that have shown little enthusiasm for sanctions. These include Greece, Cyprus and Hungary, all of which Moscow has actively courted.