Facebook has removed advertisements created and widely shared by President Donald Trump’s reelection campaign that displayed Nazi markings meant to designate political dissidents in concentration camps.

The ads included a red inverted triangle paired with text warning of “dangerous mobs of far-left groups” running around “causing mayhem.” In the 1930s, the same badge was used to identify communists, liberals, social democrats, and others who did not agree with the politics of the Nazi party. Jewish political dissenters were forced to wear the inverted triangle over a yellow star.

The ads displayed by Trump's reelection campaign asked supporters to sign a petition against antifa, a term to describe groups of relatively unorganized anti-fascist activists, which the President has recently called a terrorist organization and has worked to tie to protests against police brutality and systemic racism around the country. There is little evidence of the connection.

Nearly 90 ads with the image were viewed on Facebook between 1 million and 1.8 million times.

A Facebook spokesperson told Fortune that the company “removed these posts and ads for violating our policy against organized hate. Our policy prohibits using a banned hate group's symbol to identify political prisoners without the context that condemns or discusses the symbol.”

In a House intelligence committee hearing on June 18, Nathaniel Gleicher, head of Facebook's cybersecurity policy, explained that his company’s artificial intelligence would bank the images shared by the Trump campaign and prevent them from resurging on the platform. “We don’t allow symbols that represent hateful organizations or hateful ideologies,” he said. “You obviously want to be careful to allow someone to put up a symbol to condemn it or to discuss it. But in a situation where we don’t see either of those we don’t allow it on the platform and we remove it. That’s what we saw in this case with this ad.”

The Trump campaign, meanwhile, claimed that the symbol had been taken from images posted by antifa. The campaign linked to items being sold by a user on spreadshirt.com with the inverted triangle and the word “antifa” over it. The items were posted just five days ago by a user who says they are from Spain. The Trump campaign added that the Anti-Defamation League (ADL) did not have the image in its hate symbols database.

“I have never seen it used by antifa, and it simply does not seem plausible to me that Trump’s team has either, based on the weird image that they shared,” Michael Edison Hayden, senior investigative reporter for the Southern Poverty Law Center, told Fortune.

In a statement to Fortune, ADL CEO Jonathan Greenblatt condemned the use of the image by the Trump campaign. “Whether aware of the history or meaning, for the Trump campaign to use a symbol—one which is practically identical to that used by the Nazi regime to classify political prisoners in concentration camps—to attack his opponents is offensive and deeply troubling,” he said. “It is not difficult for one to criticize their political opponent without using Nazi-era imagery. We implore the Trump campaign to take greater caution and familiarize themselves with the historical context before doing so. Ignorance is not an excuse for appropriating hateful symbols.”

Danielle Abril contributed additional reporting to this story.