MOSCOW, May 23 (Reuters) - Russian Foreign Ministry spokeswoman Maria Zakharova said on Thursday that the European Union will feel the "full measure" of Russian retaliation over its plan to use income from frozen Russian assets to help Ukraine.

EU countries have formally adopted a plan to use windfall profits from Russian central bank assets frozen in the EU for Ukraine's defence, the Belgian government said on Tuesday.

Russia says such action is illegal and undermines the foundations of the global financial system. (Writing by Felix Light; Editing by Mark Trevelyan)