MOSCOW — Ukraine on Tuesday put in place new sanctions seeking to block Russian media and online networks from operating in the country, including VKontakte, the nation’s most popular social network.

The decision, signed by President Petro Poroshenko, was announced in an updated sanctions list, which included the Russian search giant Yandex, social media sites like Odnoklassniki, and a number of Russian state and private television channels.

The spokesman for the Kremlin described the new sanctions as unfriendly and shortsighted and warned that there could be retaliation.

The sanctions, which target the companies that run the sites, mean they cannot do business in Ukraine, but it is not clear if the country has the legal and technical means to totally block them.

As of Tuesday afternoon, the sites were still available in Ukraine. But in a statement posted online, a representative for Ukrtelekom, the country’s largest internet provider, said it would voluntarily follow the ban, and work on blocking the sites in the coming weeks.

In response to the ban, Mail.ru, an email service, posted an online tutorial in how to use Virtual Private Networks to access sites being blocked by the government.

Ukraine’s Security and Defense Council said the sanctions were in part to protect people from companies “whose activities threaten information and the cyber security of Ukraine,” according to a statement cited by Reuters news agency.

Ukraine, along with Western countries, has targeted Russia with sanctions because of Moscow’s annexation of Crimea in 2014 and material support for separatists in the country’s southeast, including with direct military means. Even before Tuesday’s additions, the sanctions list totaled more than 400 Russian entities.