Twitter CEO Jack Dorsey has apologized for a neo-Nazi ad that appeared on the site.
Dorsey tweeted Thursday that Twitter's automated system let a promoted tweet from a white supremacist group slip through. The ad has since been removed, and the group's account suspended.
"We made a mistake here and we apologize," Dorsey said.
Dorsey included a link to a Wednesday story on Motherboard that featured a screenshot of the ad and that noted it had appeared just after Twitter announced new measures to combat hate speech.
Twitter's ad gaffe follows a company crackdown on accounts associated with the alt-right movement, a fringe conservative movement that's linked to white supremacy. On Wednesday, the social network suspended the accounts of high-profile alt-right leaders, including Richard Spencer, who runs the National Policy Institute, a white-nationalist think tank.
Twitter isn't the only social network that's been plagued by hate speech. Facebook has had similar problems. To combat the issue, Facebook has a subcontractor army of "several thousand people" overseas that evaluates flagged content, according to a report Thursday by NPR. Those contractors are encouraged to move fast, with workers sometimes making decisions on content every 10 seconds, the report said.
Reached by CNET, a Facebook spokeswoman declined to say how big the overseas team is or to share any other information about the subcontractors' process for evaluating flagged content.
The episode on Thursday follows other criticisms tech giants have gotten about what they're showing on their sites and how.
Facebook and Google have been embroiled in a fake-news controversy that some people have suggested affected the outcome of the US presidential election. President Barack Obama said on Thursday the spread of false information on social media is a threat to democracy.
First published November 17, 11:52 a.m. PT.
Update, 3:27 p.m.: Adds context about Facebook's issues with hate speech.