Twitter has announced that it will stop taking advertising from all accounts owned by RT and Sputnik, effective immediately as US lawmakers continue to investigate the impact of foreign-sponsored fake news on the 2016 election.

In a blogpost on Thursday the company said it had taken the decision following its own investigations and the US intelligence community’s conclusion that both RT, formerly known as Russia Today, and Sputnik attempted to interfere with the election on behalf of the Russian government.

“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, saying that the move flouted international and domestic laws on free speech, the RIA news agency reported.

“We see this as an aggressive move,” Russian Foreign Ministry spokeswoman Maria Zakharova told the RIA Novosti agency.

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

RT’s editor-in-chief, Margarita Simonyan, attacked the move on Twitter, asking whether Twitter’s chief executive, Jack Dorsey, would explain to Congress why the company had asked the Russian service to invest in advertising around the election.

“I never thought that Twitter is under the control of the US security services – it seemed like a conspiracy theory,” she was quoted as saying. “But now Twitter appears to have admitted it.”

RT called Twitter’s statement “groundless and greatly misleading” and said that it had “never pursued an agenda of influencing the US election through any platforms, including Twitter”.

The Russian news service said Twitter had pushed RT to “spend big” during the campaign and offered it access to exclusive tools to get its message across.

The company will donate the $1.9m it has received from the Russian news sources to support external research into the “use of Twitter in civic engagement and elections”.

Twitter, Facebook and Google have all come under pressure for their roles in propagating fake news ahead of Donald Trump’s election. The company had previously announced plans to make political advertising more transparent. Those changes come as a Senate intelligence committee investigates the Kremlin’s potential meddling in US politics.

Sputnik said on its website that Twitter’s move was regrettable, “especially now that Russia had vowed retaliatory measures against the US media.” It did not elaborate.

The news came as Twitter announced it is close to posting its first ever profit after making deep cuts to jobs and expenses and finding new sources of revenue.

But growth at the social media company loved by celebrities and Trump has remained sluggish and Twitter announced it had found an error in its accounting that had overestimated the number of its users.

The social media company has never had a profitable quarter but now believes it “will likely” be profitable in the fourth quarter of this year. The good news sent the company’s share price soaring over 12% in early trading.

For the third quarter, Twitter had a revenue of $590m, down 4% from $616m a year earlier, a fall the company blamed largely on the previously announced decision to wind down its TellApart advertising product.

But the good news on profits came as Twitter once again revealed disappointing growth in the US. Twitter had 330 million monthly active users (MAUs) in the quarter ending on 30 September, up just four million from the previous quarter.

In the US the number of users rose to 69 million from 68 million.

Twitter also said that it had uncovered an error in the way it has calculated the size of its user base since 2014 and has revised its estimates downward, but that the difference amounted to less than 1%.

Twitter said the error in past user estimates was caused when it wrongly counted people who logged into applications associated with the company’s Fabric software platform, which Twitter sold this year to Alphabet’s Google.

“Yes, they grew four million MAU sequentially, which is good enough for the stock to stay at current levels, but revenue growth remains a problem,” said Michael Pachter, managing director, equity research at Wedbush Securities.

Investors and analysts have at times criticized Twitter for how it describes the size of its user base, which is a key metric for social media companies. Unlike Facebook, Twitter does not disclose how many daily active users it has.

Dorsey said in a statement that the business was making progress growing its audience and returning to revenue growth. “We’re proud that the improvements we’re making to the product continue to bring people back to Twitter on a daily basis,” he said.

Twitter’s net loss narrowed to $21m, compared with $103m, a year earlier.

The company has stepped up efforts to keep people hooked through live-streaming deals, including broadcasts of concerts, news and sports. Last month, Twitter began a test of tweets that are as long as 280 characters, double the existing cap, to allow people to better express themselves.