Jewish community centers across the nation are under siege as dozens received bomb threats this month ― including more than 20 reported on Wednesday alone.

Authorities in Ohio were on high alert after threatening calls were made to Jewish centers in Cincinnati and Columbus, Ohio. Meanwhile, centers in Florida, New Jersey, Connecticut, Massachusetts, New York and other states reported similar calls.

There’s no apparent motive and no immediate danger, said Hamilton County Sheriff’s Office Capt. Mike Hartzler, who works as the director of a joint task force between local and federal authorities in Ohio.

“For the past several weeks, there have been multiple bomb threats called into Jewish centers on the eastern side of the country,” Hartzler told The Huffington Post. “Today there were several states that received these threats, which appear to be robocalls ... Federal intelligence agencies are aware.”

The centers reported at least three kinds of calls ― those that include human voices, those that include disguised voices, and robocalls ― said Elise Jarvis, director of law enforcement outreach for the Anti-Defamation League. She confirmed that federal authorities have been briefed on the threats, but said they aren’t credible.

“Typically, these kinds of threats are a tactic used to scare the community, to disrupt operations and terrify,” Jarvis told HuffPost. “It is an intense climate right now, between a spike in hate incidents post-election and a series of bomb threats targeting the Jewish community over the past couple weeks. ... These threats are not credible, but it’s important to take each one seriously.”

Authorities wouldn’t confirm the details of those calls. The FBI told HuffPost late Wednesday that it was “investigating possible civil rights violations” in response.

The threats have put Jewish leaders on guard.

“Like many JCCs around the country this month, we received a non-credible threatening phone call earlier today,” said JCC Manhattan Executive Director Rabbi Joy Levitt. “We have worked with the proper authorities and followed all recommended procedures, ensuring the ongoing safety and security of all members of our community. As always, we will maintain communication with our security team in order to vigilantly maintain a secure building.”

On Jan. 9, more than a dozen Jewish centers in South Carolina, North Carolina, Tennessee, New Jersey, Florida, Maryland, Delaware, Georgia and Pennsylvania received anonymous bomb threats. Some of those calls were reportedly made by humans, and it’s unclear whether those incidents were directly related to the threats reported on Wednesday.

The JCC Association of North America, which oversees many of the centers that received threats on Wednesday, confirmed that the calls were similar to those received earlier this month.

“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. While the bombs in question are hoaxes, the calls are not,” said David Posner, spokesman for the association. “We know that law enforcement at both the local and national level are continuing to investigate the ongoing situation. We are relieved that no one has been harmed and that JCCs continue to operate in a way that puts the safety of their staff, visitors, and premises first.”

Correction: An earlier version of this story incorrectly stated that Arizona was among the states in which a bomb threat was received.