"My understanding is that that post did not necessarily violate that call to arms policy at the time," said Zuckerberg, referring to the Kenosha Guard's calls for people to "take up arms" and defend the city from "evil thugs."

Muslim Advocates Executive Director Farhana Khera said Zuckerberg's testimony directly contradicted what Facebook had told civil rights organizations about how its "call to arms" policy applied to the Kenosha incident.

"Facebook's constantly changing explanations of why the policy failed and how it even works adds further evidence that the company isn't serious about creating policies that will actually protect our safety and security," she said in a statement.

Facebook eventually removed the Kenosha Guard page after the shooting deaths of two people during the protests, saying it violated a separate rule against "militia organizations."

The Kenosha Guard also created a Facebook event and warned police they would be "outnumbered." BuzzFeed reported https://www.buzzfeednews.com/article/ryanmac/kenosha-militia-facebook-reported-455-times-moderators that Facebook received 455 user reports flagging that event, but that content moderators determined it did not violate the company's policies.

Zuckerberg has called that inaction an "operational mistake."

Facebook's "call to arms" policy, announced last year along with a scathing civil rights audit of the company, banned events that advocate bringing weapons to locations like schools and houses of worship to harass others based on their identity.

A Facebook spokeswoman told Reuters the policy applies to some protests, if they have a high risk for violence, but declined to respond to a question on whether the company had designated Kenosha as high risk.

In introducing the policy last year, Chief Operating Officer Sheryl Sandberg said it barred "posts from people who intend to bring weapons anywhere to intimidate or harass others, or who encourage people to do the same."

(Reporting by Katie Paul in Palo Alto and Elizabeth Culliford in Birmingham, England; editing by Richard Pullin)

By Katie Paul and Elizabeth Culliford