PHILADELPHIA (CBS/AP)–Federal authorities are now investigating threats made at Jewish community centers across the country — including one in Wilmington, Delaware.

A brief FBI statement Wednesday says it and the Justice Department’s civil-rights division are investigating “possible civil rights violations in connection with threats.” The statement from the agency’s Washington headquarters doesn’t characterize the threats.

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But the Anti-Defamation League the same day issued a statement citing “a series of bomb threats to Jewish community centers in at least 17 states.”

The ADL’s Jonathan Greenblatt adds about actual explosives that “so far these threats do not appear to be credible.” But the statement says centers should still take them seriously.

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The ADL says it’s received reports of threats in New York, New Jersey, Ohio, Florida, Massachusetts, Maryland, Michigan, Minnesota, Delaware, Connecticut, Alabama, California, Maine, Tennessee, South Carolina, Missouri, Texas and Kansas.

Last week, the Siegel Jewish Community Center in Wilmington, Delaware closed briefly due to a bomb threat. No threat was found, authorities said.

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The FBI says it is investigating, along with the Justice Department’s Civil Rights division.