"We consider this measure as totally arbitrary and unjustified, especially in the absence of any further clarification and transparency," an EU spokesperson said in a statement.
A UK Foreign Office spokeswoman told CNN, "There is absolutely no justification for this list. And the Russian authorities have not provided any legal basis for the list or for the names on it.
"If Russia thinks this action will cause the EU to change its position on sanctions, it is wrong. The way for Russia to get the sanctions lifted is to remove its troops from Ukraine and comply with its obligations under the Minsk agreements. The EU and member states are urgently seeking more transparency from the Russian authorities for this move," she added.
"We would like to refrain from comments on names of the people who were barred from entering the Russian Federation, although (their surnames) appeared in some media outlets. At the same time, we confirm that similar lists have been handed to our European partners."
He also suggested that the publication of some of the names on the list may have made matters worse, as they "were handed to our European partners as a gesture of trust and their publication may weigh on the conscience of corresponding sides.
"Just one thing remains unclear," he added. "Did our European co-workers want these lists to minimise inconveniences for potential 'denied persons' or to stage another political show?"
The official also said that the list is a direct response to EU sanctions on Russia.
"An answer to some European countries demanding to explain why these names have been put on the lists of persons banned from entering Russia is quite simple: this was done as a response to a sanctions campaign unleashed against Russia by some Germany-led countries of the European Union."
Although certain U.S. names are on the list, he said, "it should be mentioned that in this case our American partners act more constructively than the European ones."
Western sanctions on Russia have hit the country hard. Sanctions imposed over Moscow's annexation of Crimea and support for separatist rebels in eastern Ukraine cost Russia $26.7 billion in 2014, and the figure could rise to $80 billion this year, Russian Prime Minister Dmitry Medvedev said in April.
Martin Schulz, president of the European Parliament, accused Russia of not being transparent: "Despite my numerous previous official requests to the Russian authorities to make the blacklist public and communicate the clear reasons why each individual has been included there, our Members have been repeatedly stopped at the border and the European Parliament has not been officially notified which of its Members are being targeted by the sanctions," he said in a statement
He concluded that he would "speak to Russia's Ambassador to the EU" on Monday and take matters further, if necessary.
The list allegedly includes former British Deputy Prime Minister Nick Clegg.
"Nick Clegg played a leading role in the last government against Russian aggression in Ukraine," a Liberal Democrat spokesperson told CNN. "We can safely assume that Nick being banned from Russia is a reaction against this. Nick remains a fierce and vocal critic of Vladimir Putin and his regime."
Belgian politician Mark Demesmaeker tweeted his reaction
to apparently seeing his name on the list: "Putin puts me on his black list. Not welcome in Russia. Too much honour for me, Mr Putin!"
Ukraine's ambassador to the Republic of Latvia, Yevgen Perebyinis, also tweeted a sarcastic response
: "#Russia's "black list" of EU politicans is the list of most devoted friends of #Ukraine. Honoured to see 5 Latvians among them. Thank you!"
Gunnar Hokmark, a Swedish member of the European Parliament, tweeted his thoughts
on a more serious, underlying issue: "Worth to note the Putinregime fears dialogue and freedom of speech, the #Blacklist is not a show of strength but of weakness, #Russia."