The Office of the Director of National Intelligence referred to RT and Sputnik specifically in a report in January as organizations that "contributed to the influence campaign by serving as a platform for Kremlin messaging to Russian and international audiences."
Twitter pointed to that report in announcing the decision, as did California Rep. Adam Schiff, the top Democrat on the House Intelligence Committee, in praising it.
"Twitter's decision should prevent these entities from pushing Russian propaganda in front of users who may not realize the manner in which Russia employs both RT and Sputnik to spread disinformation and undermine democracies around the world," Schiff said in a statement.
The Russian government, as well as RT, responded immediately.
Russian foreign ministry spokeswoman Maria Zakharova told state media that the move was a violation of international laws that "guarantee the freedom of speech."
She added that "retaliatory measures will naturally follow," a message echoed by RT's editor-in-chief, Margarita Simonyan.
"I never thought that Twitter is under the control of the U.S. security services — it seemed like a conspiracy theory. But now Twitter appears to have admitted it," Simonyan said, to another state media agency. "This is highly regrettable. It is particularly regrettable that now U.S. media operating in Russia will feel the tender response of the Russian authorities."
RT has also been involved in a back-and-forth with the Justice Department, over whether it should register its American arm under the Foreign Agents Registration Act.
Doing so would require the company to disclose funding information and be more outwardly transparent about its relationship with the Russian government, but as CNN reports, despite a mid-October deadline request by the DOJ, there's no sign RT is planning on registering.
RT and Sputnik will be allowed to remain regular users of Twitter -- in other words, to post with normal accounts -- but they won't be allowed to pay to promote them.
Twitter added in its statement that the company would be donating the $1.9 million it is projected to have received from RT since 2011 to fund external research into the impact of Twitter on elections, with a focus on "malicious" automated bots.