Former Twitter CEO Dick Costolo reportedly censored abusive tweets directed at President Barack Obama during his #AskPOTUS digital town hall chat on the platform in May 2015, according to a report by BuzzFeed News. Citing multiple anonymous sources, including a former senior employee of Twitter, Costolo allegedly ordered employees to secretly deploy an algorithm that would weed out any abusive content directed at Obama.

In addition to the algorithm, which was reportedly built in-house and was fed thousands of examples of abusive tweets, one source alleged that the media partnerships team also censored tweets manually because the company's public quality-filtering algorithms were not as consistent.

The decision to create and use the tool was also reportedly so secretive that senior company employees were kept in the dark about the move for fear of objection.

Costolo, however, has denied the report, slamming it as "sensationalist nonsense."

"Total nonsense and laughably false as anybody who would speak on the record would tell you," Costolo tweeted on Thursday (11 August). "Absurd."

"Shows a lack of understanding of very basics of how trust and safety works at Twitter," Costolo added in a separate tweet.

Twitter has also issued a statement on Thursday in response to the report claiming there were "inaccuracies" in the story.

"In response to today's BuzzFeed story on safety, we were contacted just last night for comment and obviously had not seen any part of the story until we read it today," Twitter wrote. "We feel there are inaccuracies in the details and unfair portrayals but rather than go back and forth with BuzzFeed, we are going to continue our work on making Twitter a safer place."

"There is a lot of work to do but please know we are committed, focused, and will have updates to share soon."

One source told BuzzFeed that a similar form of censorship was allegedly implemented during a Q&A with Caitlyn Jenner as well.

"This was another example of trying to woo celebs and show that you can have civilized conversations without the hate even if you're a high-profile person," the source said. "But it's another example of a double standard — we'll protect our celebrities, while the average user is out there subject to all kinds of horrible things."

The latest revelation comes amid mounting criticism against social media networks struggling to moderate and tackle online harassment, abuse and vicious trolls on their sites whilst promoting free speech.

Recently, Ghostbusters star Leslie Jones left Twitter after facing vile sexist and racist abuse on the site and called out the company for not doing enough to deal with online abuse on its platform.

Twitter permanently banned notorious troll, Milo Yiannopoulos, accusing the conservative tech editor of American news website Breitbart News of inciting the harassment targeting Jones.