Jewish community centers and schools in at least 13 U.S. states reported receiving bomb threats on Monday, the fifth wave of such threats this year that have stoked fears of a resurgence of anti-Semitism.
The threats, all of which appeared to be hoaxes, were received in Alabama, Delaware, Florida, Indiana, Maryland, Michigan, New Jersey, New York, North Carolina, Pennsylvania, Rhode Island and Virginia, the JCC Association of North America said. For some centers, it was the second or third time this year they had been targeted.
Police in Mercer Island, Washington, also reported a community center was targeted by a bomb threat.
"Members of our community must see swift and concerted action from federal officials to identify and capture the perpetrator or perpetrators who are trying to instill anxiety and fear in our communities," David Posner, a director at the JCC Association, said in a statement.
The San Francisco office of the Anti-Defamation League, a watchdog group that monitors hate groups, received a bomb threat and was evacuated while police investigated, the Anti-Defamation League said in a statement.
Jewish groups, President Donald Trump and Israeli officials have condemned the surge in disruptive intimidation, as well as the vandalism of Jewish cemeteries.
Police said on Sunday about 100 headstones had been toppled at a Jewish cemetery in Philadelphia, about a week after a Jewish cemetery in St. Louis was vandalized.
White House spokesman Sean Spicer raised the subject at a news briefing on Monday.
"The president continues to condemn these and any other forms of anti-Semitic and hateful acts in the strongest terms," he told reporters, saying they were in breach of the country's founding principles.
The Federal Bureau of Investigation and the Justice Department's civil rights division have said they are investigating the threats alongside police, but little information has been made public about any perpetrators.
The Charles E. Smith Jewish Day School in Rockville, Maryland, and the Gesher Jewish Day School in Fairfax, Virginia, also received telephoned bomb threats, the Jewish Federation of Greater Washington said. Police later gave the all clear.
The JCC Association said there were 21 incidents of bomb threats called in to 13 JCCs and eight Jewish day schools on Monday.
Some Jewish groups see the vandalism and threats as a sign that anti-Semitic groups have been emboldened by Trump's election. His campaign last year drew the support of white supremacists and other right-wing groups, despite his disavowals of them.