Threats were reported in Georgia, Maryland, Massachusetts, New York, Oregon, Washington and Wisconsin.
The threats, which were made via phone and email, are among more than 100 across the United States and Canada since early January, according to the Anti-Defamation League.
There also have been acts of vandalism at Jewish cemeteries and several incidents in Miami where swastikas were etched into cars in what authorities are calling a disturbing pattern of anti-Semitism.
"This is not 'normal,'" Jonathan Greenblatt, CEO of the Anti-Defamation League said in a statement, "We will not be deterred or intimidated. These threats (are) in addition to threats to at least six JCCs and three day schools in Oregon, Wisconsin, Illinois, New York, Florida, Maryland and Toronto."
In Washington, a letter signed by all 100 US senators urged the Trump administration to step up security at Jewish community centers and day schools and synagogues.
Senators warn of accelerating threats
The letter from the senators said that, according to the Jewish Federations of North America, at least 98 incidents had been reported against JCCs and Jewish day schools at 81 locations in 33 states during the first two months of the year.
The senators expressed concerns about the desecration of hundreds of headstones at Jewish cemeteries in St. Louis and Philadelphia.
In the letter to Department of Homeland Security Secretary John Kelly, Attorney General Jeff Sessions and FBI Director James Comey, the senators wrote: "We are concerned that the number of incidents is accelerating and failure to address and deter these threats will place innocent people at risk and threaten the financial viability of JCCs, many of which are institutions in their communities."
In Washington, White House press secretary Sean Spicer acknowledged the new threats, telling reporters: "We'll continue to condemn them and look at ways in which we can stop them."
The FBI has said it is investigating the incidents along with the Justice Department's civil rights division.
In New York last week, a former reporter who was fired for fabricating sources was arrested and accused
of making some of the recent bomb threats against Jewish institutions.
Juan Thompson, 31, was charged with one count of cyberstalking for making at least eight threats as part of an attempt to intimidate a particular person after their romantic relationship ended, according to a criminal complaint filed in the Southern District of New York. The accusation, however, accounted for just a tiny minority of the total bomb threats received by Jewish institutions since 2017 began, according to JCC Association of North America.
New York Mayor Bill de Blasio and Police Commissioner James O'Neil on Tuesday held a closed-door meeting with Jewish leaders at a JCC on Staten Island to discuss the anti-Semitic incidents throughout the city.
"We understand history and any member of the Jewish community who feels that these threats are not only unsettling but too reminiscent of the past, they have every right to feel that and we understand that," de Blasio told reporters.
"So, our response is to be not only vigilant but aggressive. This is the stance that New York City takes and the NYPD takes in addressing hate crimes."
Gov. Andrew Cuomo on Tuesday directed the state police to coordinate with federal and local law enforcement to investigate bomb threats against New York Jewish community centers in Rochester and Syracuse and the Anti- Defamation League headquarters in Manhattan.
In a statement, Cuomo said the latest threats were a "pointed assault on the values we hold dear, and we will not allow these types of threats to continue to pervade our society. Jewish Community Centers across New York serve as a gathering place for children, seniors, friends and neighbors -- and any threat to them is an attack on all of us."
'Time for action'
The Jewish center in Syracuse tweeted that its campus received a phone threat Tuesday morning and that people there sheltered in place.
"Everyone is safe and all is ok," the center later tweeted:"Everything is back up and running normally."
In Chicago, police evacuated a Jewish grade school on the North Side because of a bomb threat Tuesday morning, authorities said.
The threat was made about 9:10 a.m. against the Chicago Jewish Day School on North Sheridan Road in the Edgewater Beach neighborhood, according to police. The school later was declared safe.
In Milwaukee, Jewish center president and CEO Mark Shapiro said the center was evacuated and delayed the start of the school day after receiving an email threat overnight. Operations resumed about 9 a.m., Shapiro said
Paul Goldenberg, national director of the Secure Community Network, which advises JCCs on security practices and has analyzed the incidents this year, said Tuesday's threats were made both over email and the phone, from live callers.
He said the latest incidents were the sixth wave this year, amounting to 140 bomb threats; each seemed different.
"It definitely has some distinguishing factors," Goldenberg said. "I think we're dealing with a mix of now potential copycats."
He added: "We are a community that's well-prepared, a community that's well trained, and our institutions are safe."