Ukraine ordered the blocking of access to a number of Russian websites Tuesday in the latest round of sanctions since Russia annexed Crimea in 2014.
Ukrainian President Petro Poroshenko has announced the closure of his official pages on Russian social media sites and urged Ukrainians to quit Russian servers for security reasons.
The Secretary of the National Security and Defense Council of Ukraine is responsible for monitoring the implementation of the decision.
In a statement, Mail.ru said it regretted the move, adding that 26 million users would be affected by the sanctions but its operations in Ukraine only made up an insignificant share of its total revenue.
"We, the VKontakte team, always avoided politics".
Mail.ru said on Tuesday that it had noticed a substantial spike in Ukrainians' use of the social media blacklisted by Poroshenko.
Yandex said it does not expect the ban to hurt the company financially but it expressed regret that "the sanctions do away with many years of hard work by our team".
President Trump Says He Had 'Absolute Right' to Share Intelligence With Russia
The source - who is in touch with current officials - says "details were discussed that should not have been discussed". The Arizona Republican said Tuesday that it sends a troubling signal to USA allies and partners around the world.
There was no immediate comment from the Russian authorities on the Ukrainian accusation.
Dmitry Peskov, Mr. Putin's spokesperson, called the sanctions "short-sighted" and warned Russian Federation had not "forgotten about the principle of reciprocity".
It was the first time Kiev restricted popular Russian-language Internet services in Ukraine, which has overseas historical and cultural connections with Russia.
The controversial order also demands that Ukrainian internet providers block all Yandex services, including its search engine and antivirus programmes DrWeb and Kaspersky Lab.
In a May 16 Facebook post, Russian Foreign Ministry spokeswoman Maria Zakharova denounced the parliament's backing of the bill as "antidemocratic and antihistorical".
Moscow has repeatedly denied accusations from Kiev that it has been waging a "cyber war" against Ukraine.
Ukraine has also accused Russian computer hackers of targeting its power grid, financial system and other infrastructure with viruses.