Anti-Semitic activities in the United States shot up an unprecedented 57 percent last year, marked by hate crimes in schools and bomb threats against Jewish institutions, according to a report released Tuesday by the Anti-Defamation League.

The ADL’s 2017 Audit of Anti-Semitic Incidents identified 1,986 examples of anti-Semitic harassment, vandalism and assault in 2017, the largest single-year increase and the second-highest number since it started tracking the data in the 1970s.

Vandalism was up by 86 percent, and incidents targeting Jewish schools, community centers, museums and synagogues had surged by 101 percent since 2016, the report found. The number of anti-Semitic incidents in K-12 schools has roughly doubled each year for the past two years, the report said.

“This is close to an all-time high,” Jonathan Greenblatt, the organization’s CEO, said in an interview, adding that the last time the number of incidents was so high was nearly 25 years ago. “Anti-Semitic activity had been going down in recent years, and we’ve started to see a shift in 2016.”

Greenblatt blamed the shift on “the divisive state of our national discourse” since the election of President Trump.

“We’re living in a time where extremists feel emboldened and they’re increasingly taking action,” he said. “They feel empowered; they almost feel like they’ve been mainstreamed.”

Anti-Semitic activity on college campuses also increased in 2017 by 89 percent to 204 incidents, the report found. That jibes with the increased visibility of white supremacist groups on campuses, which has included setting up tables, holding meetings and posting fliers, Greenblatt said, adding they have also adopted a more subtle approach to appeal to a broader audience.

“They’ve dropped the boots in favor of suits; they’ve dropped the camos in favor of khakis; they talk about white culture and supporting policies like ending immigration.”

Similarly, a Southern Poverty Law Center study released last week found that the overall number of hate groups rose last year by 4 percent.

But the numbers are probably much higher than in the ADL and SPLC reports since many hate crimes are never reported, said Heidi Beirich, director of SPLC’s Intelligence Project and overseer of its yearly count of hate groups.

“We’re in an ugly time,” she said, adding, “We’re not even close to capturing even one-tenth” of actual incidents.

While the number of anti-Semitic incidents has surged in the past couple of years, anti-Semitic attitudes have not seen a similar rise, Greenblatt said. The ADL has tracked these since the 1960s, when more than 30 percent of the population held anti-Semitic attitudes. But in recent years they have held steady at 12 to 14 percent.