Twitter has banned advertisements from the accounts of state-supported Russian media outlets Russia Today (RT) and Sputnik, citing assertions by U.S. intelligence agencies that these networks interfered with last year's U.S. presidential election.
The Russian government labeled Twitter's move "aggressive" and vowed to respond.
The ban was announced by the San Francisco-based social network in an unsigned statement on October 26 that election-meddling is "not something we want on Twitter."
"We did not come to this decision lightly, and are taking this step now as part of our ongoing commitment to help protect the integrity of the user experience on Twitter," the company said.
Russia's Foreign Ministry vowed to retaliate.
"We see this as the latest aggressive move aimed at blocking the activity of Russia Today television and coming as a result of pressure from part of the American establishment and intelligence agencies," Russian Foreign Ministry spokeswoman Maria Zakharova said on Facebook, adding, "A response will naturally follow."
In a statement on its website, RT, also known as Russia Today, said that it has never been involved in any illegal activity online and "never pursued an agenda of influencing the U.S. election through any platforms, including Twitter."
It also said on its website that Twitter's sales staff had pressured the Russian outlet in 2016 to spend big on advertising ahead of the election.
"The more money RT spent, the bigger the reach to American voters that Twitter would provide," RT said, describing the Twitter offer.
Social media firms which rely on advertising, including Twitter, generally employ sales staff to drive sales. Twitter declined to comment on any discussions with advertisers.
Sputnik, a news agency, said on its website that its "news channels are followed by people who are tired of the mainstream and who are looking for an alternative perspective on the news."
Sputnik added that Twitter's move was regrettable, "especially now that Russia had vowed retaliatory measures against the U.S. media." It did not elaborate.
Last month, Twitter said it had suspended about 200 Russian-linked accounts as it investigates propaganda efforts related to last year's election.
Facebook and Google have recently detected that suspected Russian operatives used their platforms last year to buy ads and post politically divisive content.