Twitter’s policy doesn’t explicitly state that denying violent events is against the rules, but the spokeswoman confirmed that “attempts to deny or diminish” violent events, including the Holocaust, would be removed based on the company’s interpretation of the policy.

“We strongly condemn anti-semitism, and hateful conduct has absolutely no place on our service,” she said in a statement. “We also have a robust ‘glorification of violence’ policy in place and take action against content that glorifies or praises historical acts of violence and genocide, including the Holocaust.”

Facebook announced Monday it would block posts denying the Holocaust, which saw the systematic extermination of 6 million Jews by the Nazis and their allies during World War II. The company’s move reversed a stance by Chief Executive Officer Mark Zuckerberg, who once defended such posts as examples of content he disagreed with but wanted to leave up to protect free speech. The company said it changed course after more data emerged, including a study showing almost a quarter of 18- to 39-year-old adults in the U.S. thought the Holocaust was a myth or was exaggerated.