Jewish community centers around the country were again targeted with bomb threats Wednesday morning, a week after a spate of similar threats against many centers.

Centers in at least 17 states were targeted Wednesday with bomb threats. Centers in New York, New Jersey, Ohio, Florida, Massachusetts, Maryland, Michigan, Minnesota, Delaware, Connecticut, Alabama, California, Maine, Tennessee, South Carolina, Missouri, Texas and Kansas all received threats.

We are aware of a number of bomb threats at JCCs. Js are working directly w/local authorities to make sure that people & premises are safe. — JCC Association (@JCCAssociation) January 18, 2017

Threats were made to at least seven JCCs in Florida, New Jersey, Delaware, Tennessee and North Carolina last week.

Marla Cohen, communications manager for the New-York based, JCC Association of North America said that 28 centers in 17 states have been threatened in total on Wednesday. Last week, there were 16 JCCs threatened in nine states. She said some of the threats came in as robo dialers and some were actual people. Last week, the FBI was called in, she said.

"We don’t know what’s going on. There are a lot of unknowns," Jeremy Russell, of the Jewish Community Relations Council in San Francisco told NBC Bay Area. "We are very concerned about the existence of these calls and the literal threat they are imposing on the community. We will be responding appropriately."

There were no injuries or actual explosives reported found following the earlier bomb threats.

"I think this is the world we now live in," said Molly Jo Rosen, who works at Kol Shofar synagogue in Tiburon, California. "There will be threats to religious organizations and we'll see it skewed toward certain religions more than others."

In response, the Anit-Defamation League issued a security advisory Thursday, urging all Jewish institutions nationwide to review bomb threat guidance provided by the FBI and to refer to the ADL's "18 best practices for Jewish institutional systems."

NBC Bay Area's Lisa Fernandez contributed to this report.