Police are searching for the vandals who 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 defaced.
On Monday morning, more than a dozen Jewish Community Centers (JCC) in the US received telephone bomb threats.
The threats were made to JCC locations in Alabama, Delaware, Florida, Indiana, Maryland, Michigan, New Jersey, New York, North Carolina, Pennsylvania and Virginia.
In a statement, the JCC's David Posner said that government officials "must speak out - and speak out forcefully - against this scourge of anti-Semitism impacting communities across the country".
"Actions speak louder than words. 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," the statement read.
Later on Monday, US Attorney General Jeff Sessions said the recent bomb threats against Jewish groups are "unacceptable" and a "very serious and destructive practice".
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.
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.
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."
Thousands of dollars have been raised to pay for the repairs and another $13,000 offered as a reward to catch the perpetrators.
On Saturday morning residents of a Buffalo suburb awoke to find bridges, cars, and a school playground defaced with anti-Semitic words and symbols.
At the daily press briefing White House spokesman Sean Spicer said that President Donald Trump "continues to be deeply disappointed and concerned about the reports of further vandalism at... Jewish cemeteries."
"The president continues to condemn these and any other forms of anti-Semitic and hateful acts in the strongest terms," Mr Spicer added.
President Trump has been accused by some inter-faith and tolerance charity groups of not responding forcefully enough to these and other hate attacks, which watchdog groups say 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".