"Stay alert," the FBI's field office in Newark said in a brief statement. The statement shared no specific details about the threat. FBI agents were investigating the matter, the statement said.

"We will share more information as soon as we can," the statement said.

Less than 3% of Americans are Jewish, and synagogues across the United States have long been wary of the threat of anti-Semitic attacks. This was heightened in 2018 when a man attacked congregants gathered for Sabbath services at the Tree of Life synagogue in Pittsburgh, Pennsylvania, killing 11 people with a semi-automatic rifle.

The U.S. Department of Homeland Security warned in February of heightened threats from extremist groups against synagogues, churches and historically Black colleges and universities.

New Jersey Governor Phil Murphy said in a statement that his office was "working with local law enforcement to ensure that all houses of worship are protected."