Bomb threats were called in to more than 30 Jewish organizations across the country Wednesday, community leaders said, and federal authorities said they are investigating possible civil rights violations in connection with the calls.

The calls to sites from Southern California to Florida, in at least 17 states, followed similar incidents last week, when at least 16 Jewish community centers received threatening robo-calls, according to the JCC Association of North America.

Some schools and community centers were evacuated, but no injuries were reported.

Paul Laurie, the chief operating officer of the Jewish Community Center of Greater Baltimore, said the organization received a bomb threat this week and last week, and was evacuated both times.

“It’s definitely been challenging for our staff and for our members,” he said.

After the second round of threats, national community leaders said “while we’re extremely proud of our JCCs for professionally handling yet another threatening situation, we are concerned about the anti-Semitism behind these threats,” a statement from David Posner, director of strategic performance at the association, read. “While the bombs in question are hoaxes, the calls are not,” Posner said.

In a written statement the FBI said that “the FBI and the Justice Department’s Civil Rights Division are investigating possible civil rights violations in connection with threats to Jewish Community Centers across the country. The FBI will collect all available facts and evidence, and will ensure this matter is investigated in a fair, thorough, and impartial manner. As this is matter is ongoing, we are not able to comment further at this time.”

Paul Goldenberg, the national director of the nonprofit Jewish Federation of America’s Secure Community Network, said he had been in touch with the FBI and the Department of Homeland Security about the threats from “people who want to disrupt our way of life.”

“We are back in our centers, back in our schools and back in our synagogues,” he said.

One organization that received a call, the Ronald C. Wornack Jewish Day School in Foster City, Calif., was evacuated Wednesday morning and its preschool was closed for the day, but the scene was cleared at around 12:15 p.m. local time.

Laura Toller Gardner, the chief marketing and membership officer at the Peninsula Jewish Community Center, which shares a campus with the day school, said she was encouraged by supportive messages she was receiving about the threats on social media.

“These kinds of things are so upsetting when they happen, but keep doing the things you’re doing,” she said she was told. “JCC’s are a force for love.”