The New York City-based organization found 1,986 anti-Semitic incidents last year, up from 1,267 in 2016. That's the highest total since 1994 and the largest single-year increase since the group began collecting this data in 1979.
The ADL said the sharp rise includes 952 vandalism incidents, an increase of 86 percent from 2016. The group also counted 1,015 incidents of harassment, including 163 bomb threats against Jewish institutions.
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Jonathan Greenblatt, the ADL's national director and CEO, said the "alarming" increase appears to be fueled by emboldened far-right extremists as well as the "divisive state of our national discourse."
"Less civility has led to more intolerance," Greenblatt told The Associated Press.
He also acknowledged that heightened awareness of the problem probably led to increased reporting of anti-Semitic incidents.
The ADL and other groups have reported a surge in postings of racist and anti-Semitic fliers on college campuses by extremist groups. ADL spokesman Todd Gutnick said the report's tally only counts incidents in which fliers had explicitly anti-Semitic messages.
The ADL also counted 19 anti-Semitic physical assaults last year, a 47 percent decrease from 2016.
Rabbi Shmuel Herzfeld of Ohev Sholom, the National Synagogue in Washington, said neo-Nazis in the U.S. are emboldened "in a way I have not seen in my lifetime."
"It's scary," said Herzfeld, whose synagogue received a bomb threat in April. "I think there is no question that it's on people's minds, and there is more of it out there."
The ADL is urging Congress to pass legislation to expand federal protections against bomb threats to religious institutions. The legislation, approved by the House in December, awaits action in the Senate, the ADL said.