People gather under U.S. and Israeli flags projected on the walls of Jerusalem's Old City on Sunday to show solidarity with the Pittsburgh Jewish community following the mass shooting at Tree of Life synagogue. (Menahem Kahana/AFP/Getty Images)

JERUSALEM — It was a shooting in a synagogue, an attack on the spiritual heart of the Jewish community in Pittsburgh, a message of hate for Jews everywhere, yet the ultra-Orthodox Jewish media in Israel and the country’s chief rabbis refrained from referring to Tree of Life as a house of worship Sunday, using phrases like “Jewish Center” and “unknown location” instead.

The omission was not an oversight.

Recognition of Reform or Conservative synagogues, where Jewish practices and texts often differ from those in ultra-Orthodox synagogues, is taboo. Not only do the ultra-Orthodox, also referred to as Haredim, adhere to strict gender separation, but using phones, playing music or driving to synagogue on the Sabbath is also prohibited.

“It is impossible for Haredim to recognize a Conservative or Reform synagogue as a real synagogue,” said Israel Cohen, a journalist and host on the ultra-Orthodox radio station Kol Barama.

A synagogue is a holy place where Jews observe Jewish law without exception, he said. “They can’t call the place where the attack happened a synagogue; it can only be a Jewish center.”

Authorities said Sunday that 11 people were killed when a man armed with three pistols and a semiautomatic rifle attacked the Conservative synagogue in Pittsburgh’s Squirrel Hill neighborhood.

It is the deadliest attack on Jews in the history of the United States.

The decision not to refer to Tree of Life synagogue as a house of worship underscores the conflict that exists between Israel’s deeply traditional Jews and the Jewish community in America, which is often more liberal.

In Israel, the ultra-Orthodox are a small but powerful community. Making up fewer than 12 percent of Israel’s 8.7 million people, they are also highly influential, boasting some 13 of 120 representatives in Israel’s parliament, the Knesset, and maintaining a kingmaker position in Prime Minister Benjamin Netanyahu’s ruling coalition.

Their rabbis are also charged with overseeing much of Israel’s crucial life-cycle institutions — approving all marriages, divorces and conversions to Judaism — often rejecting certification of those events when officiated by Reform or Conservative rabbis. They also serve as the gatekeepers of Israel’s key holy Jewish sites.

It is at the Western Wall — the holiest site for Jews to pray, which once made up the outer barrier of a Jewish temple built more than 2,000 years ago — where the tension between the Jewish streams is most pronounced.

Roughly one-third of American Jews identify as Reform and a further 18 percent with Conservative Judaism, a 2013 Pew study found. Only 10 percent identify as Orthodox. For years, American Reform and Conservative Jews have been pushing the Israeli government to establish an egalitarian space at the wall for their communities to pray in the same style they do in the United States.

But Netanyahu, who has long valued the support of American Jews and often refers to himself as the leader of the Jewish world, is also bound by the demands of his ultra-Orthodox coalition partners. His proposed compromise, a space at the southern end of the holy site, is seen as unacceptable by Reform and Conservative Jews.

A compromise acceptable to all Jews remains elusive, and ultra-Orthodox leaders have made no secret of their dislike for Reform and Conservative Jewish practices.

In July, Knesset member Yinon Azoulay from the ultra-Orthox Shas party, said in a debate over creating an egalitarian space at the Western Wall that Reform Jews "are not Jews.” He blamed them for causing a minor earthquake in northern Israel.

Jerusalem’s former chief rabbi, Shlomo Amar, also caused an uproar in the wall debate when he said Reform Jews were worse than Holocaust deniers.

Israel’s chief rabbis — there are two — did issue statements condemning the attack, though they stopped short of recognizing that it took place in a synagogue.

"I was shocked to hear about the murder of innocent Jews in Pittsburgh Pennsylvania, simply because they were Jews, by an abhorrent murderer who was driven by anti-Semitic hatred,” Sephardic Chief Rabbi Yitzhak Yosef said in a statement. “My heart is with the bereaved families and with all of our Jewish brothers and sisters who live in the US.”

In an interview with Makor Rishon, a newspaper aimed at the Modern Orthodox community, the country’s Ashkenazi chief rabbi, David Lau, referred to Tree of Life synagogue as “a place with a profound Jewish flavor.”

“This tragedy should bring all Jews together, not rip us further apart,” said Rabbi Rick Jacobs, president of the Union of Reform Judaism, which represents 1.5 million Reform Jews in some 900 synagogues in the United States and Canada.

“It’s unconscionable that any rabbi worth their name would question the Jewishness of those worshiping on Shabbat in a synagogue shattered by murder and the blood of Jews,” he said.

Michael Oren, Israel’s former ambassador to the United States who now serves as a deputy minister in Netanyahu’s government, also tweeted on the matter, calling on Israel to bolster the relationship with Jewish communities around the world.

“The Conservative Jews of Pittsburgh were sufficiently Jewish to be killed because they were Jews, but their movement is not recognized by the Jewish State,” Oren tweeted.