WASHINGTON (Reuters) - Facebook Inc FB.O said on Thursday it will introduce tools to prevent fake news stories from spreading on its platform, an about-face in response to rising criticism that it did not do enough to combat the problem during the U.S. presidential campaign.

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The social network company stressed that the new features are part of an ongoing process to refine and test how it deals with fake news. It has faced complaints this year involving how it monitors and polices content produced by its 1.8 billion users.

Facebook said users will find it easier to flag fake articles on their News Feed as a hoax, and it will work with organizations such as fact-checking website Snopes, ABC News and the Associated Press to check the authenticity of stories.

If such organizations identify a story as fake, Facebook said, it will get flagged as “disputed” and be linked to the corresponding article explaining why.

The company said disputed stories may appear lower in its news feed, adding that once a story is flagged, it cannot be promoted.

A few weeks ago, Chief Executive Mark Zuckerberg said it was a “crazy idea” that fake or misleading news on Facebook helped swing the election in favor of Republican Donald Trump. But criticism persisted amid reports that people in the United States and other countries have fabricated sensational hoaxes meant to appeal to conservatives.

Critics said fake news often was more widely read than news reported by major media organizations.

Ahead of the Nov. 8 election, Facebook users saw fake news reports saying Pope Francis endorsed Trump and that a federal agent who had been investigating Democratic candidate Hillary Clinton was found dead.

The effort by Facebook is intended to focus on the “worst of the worst” of clear hoaxes created by “spammers for their own gain,” Adam Mosseri, Facebook’s vice president in charge of its News Feed, said in a blog post.

Some far-right conservative writers quickly pounced on the announcement, decrying it as a covert attempt to muzzle their legitimate content.

“Translation: A group of incredibly biased left-wing fake news outlets will bury dissenting opinions,” Paul Joseph Watson, editor-at-large of the far-right website Infowars, which routinely peddles unsubstantiated conspiracy theories, said on Twitter.

Facebook has struggled throughout the year to mollify conservatives who fear the company may be censoring them. The company fired contractors who managed the site’s trending news sidebar after a report by Gizmodo in May quoted an anonymous employee claiming the site routinely suppressed conservative news.

On Thursday, Joel Kaplan, Facebook’s vice president for U.S. public policy, met with President-elect Trump at his Manhattan tower.