By David Uberti

An audit commissioned by Facebook Inc. urged it to improve artificial intelligence-based tools it uses to help identify problematic content such as hate speech, showcasing the current limits of technology in policing the world's largest social media platform.

The report, made public Wednesday, examined Facebook's approach to civil rights and criticized it as "too reactive and piecemeal," despite much-publicized investments in AI-based censors and human analysts trained to track down and remove harmful content.

Facebook says that as of March those tools helped zap 89% of hate speech removed from the platform before users reported it, up from about 65% a year earlier, according to the report. But outside researchers argue it is still impossible to gauge just how many posts escape the dragnets on a platform so large.

"I could just hop on [Facebook] right now and go to particular pages and find tons," said Caitlin Carlson, a communications professor at Seattle University who has studied hate speech on Facebook. "If the tech is getting so much better, why isn't Facebook getting so much better?"

As powerful as Facebook's AI-based tools are, removing objectionable posts isn't as easy as hitting a delete button.

Training machine-learning tools to review content as human moderators would takes time, expertise and reams of data to identify new words and imagery. Hate groups have also grown more adept at avoiding the platform's automated censors. Then there is Facebook's scale -- 2.6 billion users split between numerous languages and cultures -- and an advertising business that relies on it.

Facebook Chief AI Scientist Yann LeCun said in a March interview that he is working to develop self-supervised AI that can help mimic human attempts to grasp it all.

"Current machines don't have common sense," he said. "They have very limited and narrow function."

He said this research "is very important for Facebook [so it] can detect hate speech in hundreds of languages."

Facebook's Dangerous Organizations team, which focuses on terrorists and other organized hate groups, illustrates the hybrid approach the company has taken in response to the challenges.

The 350-person unit, spearheaded by counterterrorism experts, used a combination of manual review and automated tools to curb the reach of jihadist groups like Islamic State. Using "hashes," or digital fingerprints of content, to identify potential propaganda in real time, the team also trained machine-learning "classifiers" to learn to review posts like human analysts.

But it has proven more difficult to reorient those tools toward white supremacists, counterterrorism experts say, which tend to be more fragmented and whose irony-laced content often overlaps with right-wing political speech. Western governments also don't identify many of these groups as terrorist organizations, removing a key cue for tech companies to take action.

Those dynamics make judgments about takedowns "much harder to reach and much harder to reach in real time," said Nicholas Rasmussen, executive director of the Global Internet Forum to Counter Terrorism, a partnership between governments and tech companies including Facebook, Twitter Inc. and Microsoft Corp.

"That's the challenge that the companies face," Mr. Rasmussen said in an interview last month.

Researchers say the white supremacist terrorist attack in Christchurch, New Zealand, last year -- livestreamed and shared widely across Facebook -- illustrates the danger of one piece of content slipping through the cracks.

Facebook has since redoubled its focus on far-right groups and increasingly turned to targeted investigations by human analysts instead of AI-based tools, company officials say. That tactic resulted in the March takedown of the Northwest Front, a group that advocated for a white ethnostate in the Pacific Northwest, and the June removal of a network of accounts affiliated with the loosely knit boogaloo movement.

Executives have pointed to Facebook's growing ability to remove such content proactively as evidence of improvement, and a company spokeswoman said Wednesday the Dangerous Organizations team has increasingly focused on this area. Still, activists and advertisers have renewed their criticisms of the company's approach to content moderation amid a national dialogue about race following the killing of George Floyd in Minneapolis police custody in May.

"We have made real progress over the years," Chief Operating Officer Sheryl Sandberg said in a blog post responding to the civil rights audit on Wednesday. "But this work is never finished and we know what a big responsibility Facebook has to get better at finding and removing hateful content."

--Steven Rosenbush contributed to this article.

Write to David Uberti at david.uberti@wsj.com

Corrections & Amplifications

This article was correctde at 2:48 p.m. ET because the original version incorrectly referred to Seattle University as the University of Seattle.