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Mark Zuckerberg, Facebook chief executive, said the group would probe allegations that the social network has excluded conservative news stories from its trending topics section.

Facebook has launched a “full investigation” into a claim made by a former news curator that employees were instructed to omit particular stories about Mitt Romney, Rand Paul and other rightwing topics in the sidebar designed to show what is popular on the site.

Mr Zuckerberg said he took the report “very seriously” but the company is yet to find any evidence that it was true. Writing in a Facebook post, he said he was inviting “leading conservatives” and “people from across the political spectrum” to talk with him and share their points of view.

“I want to have a direct conversation about what Facebook stands for and how we can be sure our platform stays as open as possible,” he said. “We believe the world is better when people from different backgrounds and with different ideas all have the power to share their thoughts and experiences.”

The Facebook founder’s post came shortly after the company released the guidelines it gives to curators who work on the trending topics section. He said they had “rigorous guidelines” that “do not permit thse prioritisation of one viewpoint over another or the suppression of political perspectives”.

The document — which looks like a media style guide — focuses on how headlines should be written and lists 10 mainstream news sources, including the right of centre Fox News and The Wall Street Journal, which curators can use to decide whether a trending topic relates to a real news event.

Mr Zuckerberg received a letter from Senator John Thune, chair of the Senate commerce committee, asking a series of questions about how “Trending Topics” was compiled, after the story on tech blog Gizmodo was published earlier this week.

Gizmodo reported that one former news curator said employees were told to exclude certain topics, while many told the site they were asked to artificially bump up other topics which were not as popular.

The report sparked outrage in the US rightwing media, from the tabloid The New York Post to The Drudge Report, which accused Facebook of “leaning left”, in a reference to chief operating officer Sheryl Sandberg’s women in business book “Lean In”.