Police are searching for the vandals that damaged what one local rabbi said was nearly 500 headstones at a Jewish graveyard in Philadelphia.
Money is being raised to repair the graves and to identify and prosecute the apparently anti-Semitic attackers.
The vandalism comes less than a week after a Jewish cemetery near St Louis, Missouri, was vandalised.
And on Friday, religious slurs and swastikas were spray-painted in several neighbourhoods of Buffalo, New York.
On Monday morning, at least six Jewish Community Centers on the US East Coast - including in the Philadelphia suburbs - received telephone bomb threats, leading to building evacuations.
A man visiting his father's grave at Philadelphia's Mount Carmel Cemetery on Sunday called police after finding that approximately 100 headstones had been knocked over.
"I'm hoping it was maybe just some drunk kids," Aaron Mallin told WPVI-TV.Media captionJewish centre threat: 'Children thought they'd gone on a field trip'
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He added that it was "very disheartening" to find the damaged graves, and that he hopes that the vandalism was not motivated by anti-Semitism.
"But the fact that there's so many, it leads one to think it could have been targeted," Mr Mallin said about cemetery, which dates back to the mid-1800s.
Many of the headstones had been toppled over, and some had cracked in half.Image copyright AFP Image caption Scott Shandler (L) and Jon Lattanzio re-set a tombstone
The Philadelphia Inquirer reports that three adjacent Christian cemeteries were left undamaged.
Philadelphia Mayor Jim Kenney denounced the attackers, saying, "my heart breaks for the families who found their loved ones' headstones toppled... Hate is not permissible in Philadelphia."
Israeli Foreign Ministry spokesman Emmanuel Nahshon posted a statement on Twitter saying, "#Philadelphia Jewish cemetery desecration is shocking and a source of worry. Full confidence #US authorities catch and punish culprits."
So far over $11,000 has been raised online to be donated to the Jewish Federation of Greater Philadelphia, in order to repair the desecrated graves.
A reward of $10,000 is also being offered by the Anti-Defamation League for information leading to the arrest and conviction of those responsible.
The local chapter of Fraternal Order of the Police, a law enforcement labour union, is offering another $3,000.
On Saturday morning residents of a Buffalo suburb awoke to find bridges, cars, and a school playground defaced with anti-Semitic words and symbols.
Local residents are trying to raise $5,000 online in order to spare the school from having to pay the cost of removing the graffiti.
"South Davis Elementary [school] shouldn't have to take money out of classrooms because of these thoughtless and hurtful actions," one concerned resident wrote in an online fundraising drive.Media captionAerial shots show headstones toppled at St Louis Jewish cemetery
President Donald Trump has been criticised by some inter-faith and tolerance charity groups for not responding with enough force to these and other hate attacks, which watchdog groups feel are happening with increased frequency.
The FBI is currently investigating over 50 hoax bomb threats phoned into Jewish Community Centres in at least 26 states since the beginning of January.
"Mr. President, it's time for you to deliver a prime-time nationally televised speech, live from the Oval Office, on how you intend to combat not only #Antisemitism but also Islamophobia and other rising forms of hate," the Anne Frank Center for Mutual Respect wrote on Twitter after the Philadelphia vandalism.
After several days of silence, Mr Trump denounced the vandalism of the Chesed Shel Emeth cemetery in St Louis, where about 150 graves were desecrated last week.
Vice-president Mike Pence also visited the St Louis graveyard, where he denounced the "vile act of vandalism" and said "there's no place in America for hatred or acts of prejudice or violence or anti-Semitism".
Hate crimes in the USMedia captionTrump says 'ugly' anti-Semitism must stop
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