Facebook on Tuesday denied allegations from a former news curator that it scrubs its site of articles by and about political conservatives.
Tech news outlet Gizmodo reported Monday that a former news curator at the social media giant has alleged that articles from politically conservative outlets - particularly when written about conservative subjects - were deliberately omitted from Facebook's "trending news" sidebar of popular stories.
"I'd come on shift and I'd discover that CPAC (Conservative Political Action Conference) or (former presidential candidate) Mitt Romney or (radio talk show host) Glenn Beck or popular conservative topics wouldn't be trending because either the curator didn't recognise the news topic or it was like they had a bias," the individual told Gizmodo anonymously.
The charges unleashed a fierce debate in the US media and on the social network itself, which has some 1.6 billion users around the globe.
But the Silicon Valley-based Facebook, a dominant player in the social media world, denied having an anti-conservative bias.
"We take these reports extremely seriously, and have found no evidence that the anonymous allegations are true," wrote Tom Stocky, vice president of search at Facebook, where he oversees the team responsible for engineering and designing Trending Topics.
"Facebook is a platform for people and perspectives from across the political spectrum," Mr Stocky wrote on the site.
The company said the popularity of news stories is determined by an algorithm, then audited - never manipulated - by review team members to confirm that the topics are in fact trending news items.
"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," Mr Stocky said.
"We want to encourage that robust political discussion from all sides."
Facebook dismissed charges, also made anonymously, that it manipulated #BlackLivesMatter so that it would become a trending topic.
"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," said Mr Stocky.