Twitter announced on Thursday that it would ban RT and Sputnik, the two Kremlin-backed international news outlets, from advertising on its platform, intensifying the battle over Russian propaganda on social media and prompting an immediate threat of retaliation from the Russian Foreign Ministry.

The decision marks one of the most aggressive moves by an American social media company against the outlets, which United States intelligence officials have linked to a wide-ranging Kremlin effort, both covert and overt, to disrupt the 2016 presidential election. Twitter’s ban comes as United States authorities are pressuring RT, formerly known as Russia Today, to register as a foreign agent under a World War II-era law intended to curtail Nazi propaganda.

“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 in a blog post announcing the ban. The ban will not apply to any other advertisers, Twitter said, and RT and Sputnik will be allowed to retain their own Twitter accounts and followers.

RT’s editor in chief, Margarita Simonyan, called Twitter’s decision “highly regrettable” and cast it as part of a punitive campaign by the United States government against her own country. Earlier on Thursday, Ms. Simonyan taunted Twitter on its own platform, tweeting that the company had pitched RT on a large advertising campaign for the 2016 election that RT had declined.