Twitter says that it will ban ads from two Russian media organisations, citing allegations by US intelligence agencies that Russia Today (RT) and Sputnik tried to interfere with the 2016 presidential election in the US.

“Twitter has made the policy decision to off-board advertising from all accounts owned by Russia Today (RT) and Sputnik, effective immediately,” the San Francisco-based company said on its website on Thursday.

The site said the decision was based on its own investigations of RT and Sputnik as well as the “US intelligence community’s conclusion that both RT and Sputnik attempted to interfere with the election on behalf of the Russian government”.

RT and Sputnik condemned the move, and Moscow threatened retaliatory measures.

The ban comes a month after Twitter officials told the US senate that it has suspended 201 Russian-linked accounts amid a congressional investigation into alleged Russian interference in the 2016 election.

US intelligence officials suspect social networks may have contributed in Moscow’s alleged propaganda attempt to help elect President Donald Trump. Russia denies the allegation and Trump has also denied any collusion.

In its statement on Thursday, Twitter said it did not “come to this decision lightly”.

It also said it will donate the estimated $1.9m it had earned from RT since 2011 to “support external research into the use of Twitter in civil engagement and elections, including use of malicious automation and misinformation”.

RT and Sputnik may remain “organic users on our platform, in accordance with the Twitter rules,” it said.

In response, Sputnik called Twitter’s decision “regrettable”, while RT said it had “never been involved in any illegal activity online” and “never pursued an agenda of influencing the US election through any platforms, including Twitter”.

RT also said Twitter had encouraged it to “spend big” on advertising in advance of the election.

“The main idea pitched by Twitter to RT was ‘to take a stand’. The more money RT spent, the bigger the reach to American voters that Twitter would provide,” it said on its website.

Maria Zakharova, a spokeswoman for Russia’s foreign ministry, said in a Facebook post that the ban was “an unprecedented attack” and a “gross violation” of free speech guarantees.

“This is the result of pressure from the American establishment and intelligence services,” she said, adding, “Retaliatory measures will naturally follow”.