A report by Gizmodo said staff responsible for what was shown to Facebook’s 1.6bn users frequently chose to bury articles they did not agree with.

Responding to the allegations, the network’s head of search Tom Stocky wrote that the site “found no evidence that the anonymous allegations are true”.

The claims come weeks after Facebook founder Mark Zuckerberg publicly denounced the policies of likely US presidential nominee, Donald Trump.

“I hear fearful voices calling for building walls and distancing people they label as ‘others.’,” the 31-year-old said at his firm’s recent developers conference.

However, Facebook insisted Mr Zuckerberg’s view did not influence what stories are given added visibility on the network.

Drudge Report, Breitbart, Washington Examiner, and Newsmax are among the conservative new organizations that allegedly were flagged as suspect by Facebook curators.

“We take allegations of bias very seriously,” Facebook said in a statement. “Facebook is a platform for people and perspectives from across the political spectrum. Trending Topics shows you the popular topics and hashtags that are being talked about on Facebook. There are rigorous guidelines in place for the review team to ensure consistency and neutrality. These guidelines do not permit the suppression of political perspectives. Nor do they permit the prioritization of one viewpoint over another or one news outlet over another. These guidelines do not prohibit any news outlet from appearing in Trending Topics.”

A post on Facebook’s help center said that the “trending” section of the site “shows you topics that have recently become popular on Facebook.” It lists “engagement, timeliness, Pages you’ve liked and your location” as some of the factors that determine what trends show up for each Facebook user.

Facebook users can also manually remove certain topics from their trending list.

Here’s Stocky’s full statement:

“My team is responsible for Trending Topics, and I want to address today’s reports alleging that Facebook contractors manipulated Trending Topics to suppress stories of interest to conservatives. We take these reports extremely seriously, and have found no evidence that the anonymous allegations are true.

Facebook is a platform for people and perspectives from across the political spectrum. There are rigorous guidelines in place for the review team to ensure consistency and neutrality. These guidelines do not permit the suppression of political perspectives. Nor do they permit the prioritization of one viewpoint over another or one news outlet over another. These guidelines do not prohibit any news outlet from appearing in Trending Topics.

Trending Topics is designed to showcase the current conversation happening on Facebook. Popular topics are first surfaced by an algorithm, then audited by review team members to confirm that the topics are in fact trending news in the real world and not, for example, similar-sounding topics or misnomers.

We are proud that, in 2015, the US election was the most talked-about subject on Facebook, and we want to encourage that robust political discussion from all sides. We have in place strict guidelines for our trending topic reviewers as they audit topics surfaced algorithmically: reviewers are required to accept topics that reflect real world events, and are instructed to disregard junk or duplicate topics, hoaxes, or subjects with insufficient sources. Facebook does not allow or advise our reviewers to systematically discriminate against sources of any ideological origin and we’ve designed our tools to make that technically not feasible. At the same time, our reviewers’ actions are logged and reviewed, and violating our guidelines is a fireable offense.

There have been other anonymous allegations — for instance that we artificially forced ‪#‎BlackLivesMatter‬ to trend. We looked into that charge and found that it is untrue. We do not insert stories artificially into trending topics, and do not instruct our reviewers to do so. Our guidelines do permit reviewers to take steps to make topics more coherent, such as combining related topics into a single event (such as‪#‎starwars‬ and‪#‎maythefourthbewithyou‬), to deliver a more integrated experience.

Our review guidelines for Trending Topics are under constant review, and we will continue to look for improvements. We will also keep looking into any questions about Trending Topics to ensure that people are matched with the stories that are predicted to be the most interesting to them, and to be sure that our methods are as neutral and effective as possible.”