Facebook removed a series of President Trump’s campaign ads on Thursday, claiming it violated the company’s policy against organized hate. The ads included an inverted red triangle, a symbol that was used by Nazis to identify political prisoners in concentration camps.

A Facebook spokesperson told CNN Business that “We 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.”

The ads first appeared on June 17, and their use of the triangle was quickly noticed. A journalist for Fortune magazine was among the first of many news outlets to bring the ads and their use of a Nazi symbol to Facebook’s attention. Despite being up for only a single day, they made more than a million impressions on Facebook.

The Trump campaign defended its use of the symbol, stating that the red triangle is a common symbol of Antifa and that “It is not in the ADL’s [Anti-Defamation League] Hate Symbols Database.”

Jonathan Greenblatt, the chief executive of the Anti-Defamation League, responded to the Trump campaign’s statement, explaining that the organization’s database tracks active hate symbols and does not track historical symbols of hate. He went on to condemn the campaign by saying that, “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 continued by adding that, “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.”

There has also been harsh condemnation of the campaign’s assertion that the symbol is commonly used by Antifa in the US.

The now-removed ads were part of a larger group of ads that targets Antifa and other far-left groups. They decry the predominantly peaceful protests sweeping the nation, calling them “Dangerous MOBS of far-left groups” that are “DESTROYING our cities and rioting.”