Facebook is changing its powerful news feed in an effort to stamp out fake stories following a firestorm around the social network's role in spreading false information.

The new features, rolled out to select U.S. users Thursday, add options for readers and third-party fact checkers to flag articles, tweak Facebook's algorithm and provide more restrictions on advertising.

A month ago, Chief Executive Mark Zuckerberg said these changes were coming, responding to extensive criticism in the wake of the U.S. presidential election.

The issue has only grown more heated since. A Pew Research Center survey, released Thursday, revealed that almost one-quarter of Americans believed they shared fake news and a greater percentage were concerned about its consequences.

Fake news stories touch on a broad range of subjects, from unproven cancer cures to celebrity hoaxes and backyard Bigfoot sightings. But fake political stories have drawn outsized attention because of the possibility that they influenced public perceptions and could have swayed the U.S. presidential election.

There have been dangerous real-world consequences. A fake story about a child sex ring at a Washington, D.C., pizza parlor prompted a man to drive from North Carolina to investigate the allegations and fire an assault rifle inside the restaurant.

Still, Facebook framed its moves carefully, showing its aversion to being seen as taking an editorial or political stance.

“Fake news means different things to different people,” said Adam Mosseri, Facebook's vice president of product management. “What we're focused on is the worst of the worst. We're not looking to get into the gray area of opinion.”

Two of the incoming changes are visible. Facebook users will be able to flag content on the site as a “fake news story.” Articles deemed false by Facebook's partner, Poynter Institute's International Fact-Checking Network, will have a new tag attached: “Disputed by 3rd Party Fact-Checkers.”

Publishers behind these articles will no longer be able to promote these articles as Facebook paid ads.

But Facebook isn't scrubbing these articles from its site altogether. “If something is been disputed, we're going to let you know,” Mosseri said. “But you can still share it because we believe in giving people a voice.”

Facebook also said it's taking steps to snip financial incentives for publishers of fake news. It plans to cut off producers of content from hoax domains from buying on its ad networks. Mosseri said these websites represent a negligible part of Facebook's advertising revenue.

Mosseri noted that the adjustments are algorithmic and won't rely on editors employed by Facebook. He also dismissed the likelihood that users would take advantage of the new features to bombard articles or publications they disagree with, rather than those stories they find blatantly false.

These incidents “happen many times less — orders of magnitude less,” Mosseri said. “Most people aren't going to report anything negative.”

Associated Press contributed.