Facebook reportedly allowed for marketers to target their ads towards users under a number of anti-Semitic categories including "Jew hater" Reuters/Dado Ruvic

Facebook allowed marketers to specially target their ads on the platform towards users interested in anti-Semitic topics "How to burn Jews" or "History of 'why Jews ruin the world." According to an investigation by ProPublica, ads on the popular social media site could be directed towards Facebook users who fell under categories such as "Jew hater", "German Schutzstaffel", also known as the Nazi SS, "Nazi Party", and "Hitler did not nothing wrong."

To test the feature, ProPublica bought $30 worth of "promoted posts" targeting these specific ad categories. Within just 15 minutes, the three ads were reportedly approved.

"A few days later, Facebook sent us the results of our campaigns. Our three ads reached 5,897 people, generating 101 clicks, and 13 "engagements" — which could be a "like" a "share" or a comment on a post," ProPublica said.

The outlet also noted that these categories were relatively small with a few thousand people for some. Slate, which did a follow up test, found that Facebook also enabled targeting for other hateful groups such as the Ku Klux Klan.

Facebook took down the offensive categories after the outlet reached out to them for comment. These categories were created by a Facebook algorithm, rather than people, and generated based on the information users plug in when filling out their profiles on the site such as employer or "field of study".

The company said it would look into ways to fix the issue such as limiting the number of categories available to marketers and having them scrutinized before they are made available to buyers.

"We don't allow hate speech on Facebook," Rob Leathern, product management director at Facebook said in a statement. "However, there are times where content is surfaced on our platform that violates our standards. We know we have more work to do, so we're also building new guardrails in our product and review processes to prevent other issues like this from happening in the future."

The revelation comes as Facebook faces intense scrutiny over its ad practices after disclosing it sold $100,000 (£74,470) worth of ads to fake accounts likely linked to Russia during the 2016 election season. The ads in question promoted divisive political messages on key issues such as immigration, race and LGBT rights.

The company has also drawn fierce criticism over its failure to curb the spread of fake news, misinformation and hoaxes on the site during the race to the White House. Initially, CEO Mark Zuckerberg dismissed critics' assertion that Facebook helped sway the vote in President Donald Trump's vote as a "pretty crazy idea".

Earlier this week, it was reported that Russian operatives used Facebook's Events feature to organise political protests in the US, including an anti-immigrant, anti-Muslim rally in Idaho in August 2016. Facebook said it shut down "several promoted events" as part of its take down of "Russian-affiliated pages" last week.

Jonathan Greenblatt, CEO of the Anti-Defamation League, praised Facebook in a tweet for taking action but said he would be contacting the social media giant for more information.

"It was shocking to read about this practice on Facebook, and we are glad Facebook ended it," he wrote. "I will be calling Facebook as soon as possible for an explanation of what went on, and will work with them to root out anti-Semitism and hate online."