Facebook made an “operational mistake” this week in failing to remove a page that encouraged armed Americans to take to the streets of Kenosha, Wisc., CEO Mark Zuckerberg said.

The page clearly violated Facebook’s rules against violent militias, Zuckerberg acknowledged in a video posted Friday to his Facebook profile, and that “a bunch of people” had even reported the page prior to the killing of two protesters, Joseph Rosenbaum and Anthony Huber.

Just last week, Facebook announced it would crack down on militia organizations that advocated for violence or spoke about the potential for violence. But in its first week of implementation, the policy’s lack of enforcement led to the spread of violent messages on the platform directly linked to the events in Kenosha, where protests erupted after the police shooting of Jacob Blake.

“What’s going on in Kenosha … is really deeply troubling,” Zuckerberg said in the video.

BuzzFeed News was first to report Zuckerberg’s remarks, before he posted the video.

A Facebook investigation of the militia page turned up no evidence that the page or the event it promoted had any connection to the 17-year-old accused of committing the killings, Zuckerberg said.

But the Facebook contractors who received the initial reports from users about the militia page did not “pick it up,” he said.

“On second review, doing it more sensitively, the team that’s responsible for dangerous organizations recognized this violated the policies, and we took it down,” Zuckerberg said.

But by then, the armed event the page was promoting had received at least 2,600 responses and had caught the attention of at least one right-wing conspiracy website.

Zuckerberg said Facebook is now “proactively out there looking for content” that praises the shooting.

“We’re going to continue to enforce our policies,” he said, “and continue evolving the policies to be able to identify more potential dangerous organizations, and improve our execution in order to keep on getting ahead of this.”