The Russian Foreign Ministry said Wednesday it had barred entry to a German member of the European Parliament because her name was on a blacklist of officials who had a role in imposing sanctions on Moscow over Ukraine.
Rebecca Harms was refused entry to Russia last week, where she was hoping to attend a court hearing for a Ukrainian officer captured by pro-Russian rebels in east Ukraine and now held in Moscow.
The conflict in east Ukraine has strained ties between Moscow and the West, including the European Union, which imposed sanctions on Russia for its role in the crisis.
Moscow denies that is has armed rebels fighting to split east Ukraine from Kiev or sent troops to help them, against what the West says is irrefutable evidence.
Harms, co-chair of the Greens group in the European Parliament, had said she believed her name to be on such a blacklist.
"This case is directly related to the existence of such a list," state-run news agency RIA Novosti quoted Russian Deputy Foreign Minister Alexei Meshkov as saying.
"Those who introduced sanctions against Russian officials, including the leaders of our parliament, should have been fully aware that Russia has an adequate response."
The EU condemned Russia's decision to bar Harms.