Earlier this week, Twitter introduced a handful of new tools in an effort to shake off its reputation as a platform rife with trolls, bullies, and abuse. But CEO Jack Dorsey has been forced to apologize after an ad promoting a white supremacy group appeared just hours after the new features came into effect.

Los Angeles musician and writer Ariana Lenarsky first spotted the promoted tweet, which came from an account associated with a neo-Nazi organization called New Order. It linked to an article on the group’s website, titled “The United States Was Founded as a White People’s Republic.” You can see her NSFW tweet here.

Twitter told Motherboard that Lenarsky's screenshot was either old or photoshopped. She responded with: “I am heartbroken that my favorite site is a coward and loves Nazis and told the news I am a liar and a photoshopper.”

Yesterday, Twitter boss Jack Dorsey posted an apology. He admitted the ad was real and his company made a mistake. The CEO blamed Twitter’s automated system for failing to flag the offending post. “We made a mistake here and we apologize. Our automated system allowed an ad promoting hate. Against our policy. We did a retro and fixed!” he tweeted. The ad and the user who posted it has since been suspended.

Not long after Twitter introduced its anti-troll measures, a number of “alt-right” users found themselves banned from the service, including head of the National Policy Institute, Richard Spencer. "Twitter is trying to airbrush the alt-right out of existence," he said.

As retaliation for the bans, white supremacists have vowed to create thousands of ‘fake black people’ accounts with the apparent aim of stirring up racial tensions.