The criticism came following a discussion involving the Facebook CEO and leaders of rights organizations to discuss the platform's hands-off policy on Trump's posts after Twitter flagged or reduced the visibility of similar comments.

"We are disappointed and stunned by Mark's incomprehensible explanations for allowing the Trump posts to remain up," said a statement from three leaders: Vanita Gupta of the Leadership Conference on Civil and Human Rights, Sherrilyn Ifill of the NAACP Legal Defense and Educational Fund, and Rashad Robinson of Color of Change.

"He did not demonstrate understanding of historic or modern-day voter suppression and he refuses to acknowledge how Facebook is facilitating Trump's call for violence against protesters. Mark is setting a very dangerous precedent for other voices who would say similar harmful things on Facebook."

The comments follow a series of protests from Facebook employees disputing the company's position of refraining from moderating the president's posts.

Social platforms have faced calls to label or remove Trump's comments which warned against fraud in mail-in voting, and which appeared to encourage violence against those protesting the police killing of a black man in Minnesota.

Over the weekend, Zuckerberg said he believes Facebook "should enable as much expression as possible unless it will cause imminent risk of specific harms or dangers spelled out in clear policies."

Facebook said it welcomed the call late Monday which included the activists as well as Facebook's chief operating officer Sheryl Sandberg.

"We're grateful that leaders in the civil rights community took the time to share candid, honest feedback with Mark and Sheryl," a Facebook spokesperson said in a statement.

"It is an important moment to listen, and we look forward to continuing these conversations."

In the latest sign of turmoil at Facebook, software engineer Timothy Aveni announced his resignation from the company, claiming Zuckerberg did not keep his word about stopping posts that glorify violence.

"Facebook will keep moving the goalposts every time Trump escalates, finding excuse after excuse not to act on increasingly dangerous rhetoric," Aveni wrote on his Facebook page

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