White supremacists have targetted Jewish institutions in America “at least 50 occasions" in the year since the Pittsburgh synagogue attack, the Anti-Defamation League (ADL) has said.

The report was released in the run up to the first anniversary of the attack on the Tree of Life synagogue, which took place on October 27, 2018 and left eleven dead and seven injured.

The ADL also added that there have been at least twelve arrests of white supremacists for their roles in terrorist plots, attacks or threats against Jews.

“Many of the offenders were inspired by previous white supremacist attacks,” the report stated. It also listed all those arrested, including Conor Climo – who plotted to attack synagogues and an LGBT bar in Las Vegas – and James Reardon, who threatened a local Jewish community centre in Ohio in a video.

“It is horrifying that in the year since the deadliest antisemitic attack in U.S. history, at least a dozen white supremacists were arrested after threatening to target Jewish houses of worship,” ADL chief executive Jonathan Greenblatt said.

“We are tremendously grateful to local, state and federal law enforcement for taking these cases seriously and preventing further bloodshed against the Jewish community.”

The report comes as police are investigating a swastika being drawn outside a Jewish attorney’s office in Palm Springs, California as a hate crime.