KIEV, May 16 – President Petro Poroshenko on Monday ordered the blocking of access to Russia's most popular social media websites and search engines as part of sanctions approved for the annexation of Crimea.

Russia is known to have used computer hacking as part of its ‘hybrid warfare’ against Ukraine, including the use of infected smart phone applications allowing Russian military to target Ukrainian artillery units in 2014 and 2015.

Russian security agencies are also believed to have been widely using Russian-based social networks for intelligence gathering, as well as for spreading fake news as part of efforts to sway political mood in the country.

A decree by Poroshenko expanded sanctions to include 468 companies and 1,228 people, including Russian social networks VKontakte and Odnoklassniki, the email service Mail.ru and the search engine Yandex.

The decree requires internet providers to block access to the sites, which are some of the most popular in Ukraine, for three years.

Poroshenko’s decree also blocked the site of the Russian cybersecurity giant Kaspersky Labs and will ban several major Russian television channels and banks, as well as the popular business software developer 1C.

In a post on his official page on VK, Poroshenko said he had tried to use Russian social networks to fight Russia’s “hybrid war” and propaganda. But Russian cyber-attacks, including its alleged interference in the French election this month, “show the time has come to act differently and more decisively”, he said, declaring he would shut down his pages on the networks, The Guardian reported.

Most of the internet and media companies banned by Ukraine are privately owned and have grown over the past decades from start-ups working out of a basement to major international businesses.

Yandex, a NASDAQ-traded company that posted $14.5 million in net profit in the first quarter of the year, in a statement on Tuesday described the ban as "sanctions against 11 million Ukrainian users who use our services, against thousands of Ukrainian companies that use our technology and service to develop their businesses," The Associated Press reported.

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."

Kaspersky Lab said in a statement that it expects its products such as anti-virus software to be available in Ukraine despite the ban. (gu/ez)