Facebook is stepping up its efforts to fight fake news by sending more suspected hoax stories to fact-checkers and publishing their findings online.

The move follows mounting criticism of the social media firm for not doing enough to root out fake news on its platform.

It has also just launched a new feature in four countries that will publish alternative news links beneath problematic articles.

The firm has previously been reluctant to take down potentially fake news stories, arguing that it does not want to be an "arbiter of truth".

Facebook identifies potentially false stories through a mixture of artificial intelligence (AI) and user detection. These are then sent to independent fact-checkers who place a flag next to hoax stories to alert readers.

On Thursday, however, the firm said it would start using "updated machine learning" to enhance detection.

"If an article has been reviewed by fact checkers, we may show the fact-checking stories below the original post," added Sara Su, product manager of News Feed, in a blog.

These stories would not be "direct responses" to fake articles, but factually accurate reports that offered an alternative.

On Thursday, the firm also rolled out a new "Related articles" feature in the US, France, Germany and the Netherlands.

The feature places links to other news coverage beneath highly popular or questionable stories, offering users "more perspectives and additional information".