Organizers of the national campaign to fill up synagogues across the United States in solidarity with victims of the Pittsburgh massacre say initial reports show that Jewish prayer houses were crowded as never before over the weekend.

According to the American Jewish Committee, which spearheaded the #ShowUpForShabbat campaign, the “vast majority of synagogues in America likely participated.” The campaign was held to commemorate the 11 victims of a shooting at a Conservative synagogue during prayer services the previous Saturday morning and to demonstrate resilience in the face of terror. It urged synagogues to open their sanctuaries to non-Jews as well.

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Avi Mayer, assistant executive director of the AJC, said that thousands of individuals from more than 75 countries – including Bahrain, Morocco and Myanmar – either indicated that they planned to participate in the campaign or expressed their support for it on the AJC website.

According to figures compiled by the AJC, the campaign was viewed around a quarter of a billion times on social media – 150 million times on Twitter and Instagram and another 100 million times on Facebook.

Mayer said that it was impossible to know exactly how many individuals attended services this past Shabbat, “but we have seen and heard countless reports of standing-room-only crowds at synagogues across the country and around the world.”

He added: “Many people said it was the most crowded they’ve ever seen their synagogues, far more than on the High Holy Days. We also heard from many who said it was either the first time they ever set foot in a synagogue – many of those were non-Jews – or the first time since their bar or bat mitzvahs.”

The campaign was endorsed by the Reform, Conservative and Orthodox movements – the three main streams of Judaism in the United States. Among those to throw their public support behind the initiative were Prime Minister Benjamin Netanyahu, former British Prime Minister Tony Blair, U.S. Speaker of the House Paul Ryan, virtuoso violinist Itzhak Perlman, Jewish-American celebrity Mayim Bialik, and publisher and writer Arianna Huffington.

Among those who responded to the campaign by attending synagogue services this past Shabbat were senators Elizabeth Warren, Chuck Schumer, Bob Menendez and Ben Cardin, as well as mayors Bill de Blasio of New York, Eric Garcetti of Los Angeles and Sadiq Khan of London.