Federal authorities were investigating a wave of bomb threats at 10 Jewish community centers across the country on Monday, the FBI said.
In a statement, the bureau said it was helping investigate the threats as possible civil rights violations. The Justice Department's Civil Rights Division was also investigating.
Centers in Alabama, Ohio, Illinois, Wisconsin, Minnesota, Florida, New Mexico, Tennessee, Texas and New York reported phoned-in threats, the Jewish Community Center Association of North America told NBC News.
No one was injured, and the threats appeared to be hoaxes, the association said.
In Missouri, more than 100 headstones were found toppled over or damaged at a historic Jewish cemetery over the weekend, NBC station KDSK of St. Louis reported — an apparent crime that quickly drew the fury of Sen. Claire McCaskill, D-Missouri.
"Please catch the hateful, evil people who did this," she wrote on Twitter. "This is not normal. Or acceptable. This is not what America stands for."
White House Press Secretary Sean Spicer said earlier that "hatred and hate-motivated violence of any kind have no place of any kind in a country founded on the promise of individual freedom," while Ivanka Trump, the president's daughter, wrote this on Twitter: "America is a nation built on the principle of religious tolerance. We must protect our houses of worship & religious centers. #JCC"
The events come just weeks after another round of bomb threats targeted 53 Jewish community centers across 26 states and one Canadian province during three days in January.
Ryan Lenz, a senior writer with the nonprofit Southern Poverty Law Center, which monitors hate groups, told NBC News that the threats coincided with what appeared to be a spike in hate speech and hate group activity since Donald Trump's election.
"We don't know who's behind these threats," Lenz said. "We don't know if groups are organizing them. We do know they're in line with an increase in hate incidents and bias incidents over the last three months."
The center counted 1,094 incidents in the 34 days after Nov. 8, from anti-Semitic and anti-immigrant to anti-LGBT and anti-black expressions.
An SPLC report released last week found that anti-Muslim hate groups operating in the United States had grown the most in recent years — up from 34 in 2015 to 101 last year. Lenz said the bomb threats were "the logical next step as this continues to escalate."
On Monday, the Anti-Defamation League issued a security advisory warning Jewish institutions across the United States to review the organization's security manual and bomb threat guidance assembled by the FBI and the Department of Homeland Security.
"We look to our political leaders at all levels to speak out against such threats directed against Jewish institutions, to make it clear that such actions are unacceptable, and to pledge that they will work with law enforcement officials to ensure that those responsible will be apprehended and punished to the full extent of the law," the group's chief executive, Jonathan Greenblatt, added in a statement.