NEW YORK (Reuters) - Hate crimes in nine U.S. metropolitan areas rose more than 20 percent last year, fueled by inflamed passions during the presidential campaign and more willingness for victims to step forward, a leading hate crimes researcher said on Monday.

Bias crimes appeared to increase in some cities following the Nov. 8 election of President Donald Trump, a trend that has extended into this year with a wave of bomb threats and desecrations at synagogues and Jewish cemeteries, according to California researcher Brian Levin.

The White House could not be reached immediately for comment on the research.

Levin collected data as director of the nonpartisan Center for the Study of Hate & Extremism at California State University, San Bernardino, where he is a professor of criminal justice. The new numbers, collected from police departments, reverse a trend toward fewer hate crimes in many of the cities in recent years.

Among U.S. cities, New York reported the greatest number of hate crimes at 380, a 24 percent increase from 2015, while Washington, D.C., had the largest percentage rise at 62 percent to 107 incidents.

Overall, there were 1,037 incidents, a 23.3 percent increase from the previous year in the nine areas researched: New York; Washington; Chicago; Philadelphia; Montgomery County, Maryland; Columbus, Ohio; Seattle; Long Beach, California; and Cincinnati.

Trump in recent weeks has more forcefully denounced the anti-Semitic and other racially motivated incidents, notably at the start of his address to Congress on Feb. 28. Trump has also expressed how he was personally affected, since his daughter Ivanka converted to Judaism and he has Jewish grandchildren.

After the most recent bomb threats last week, the Trump administration denounced them “in the strongest terms,” White House spokesman Sean Spicer said, promising to search for ways to stop them.

While some Jewish leaders have suspected the bomb threats may be linked to a higher profile for white nationalists animated by the Trump’s campaign, Levin did not draw that direct link.

In New York City alone, there were 55 anti-Semitic crimes reported from Jan. 1 to March 5 this year, up 189 percent from 19 such incidents in the same period of 2016, the data showed.

“We might very well be at the start of a trend where anti-Semitic incidents are going up each year. We were seeing an over-decade decline in anti-Semitic incidents,” Levin said.

Bias crimes against Muslims and lesbian, gay, bisexual and transgender people accounted for much of the growth in hate crimes that were reported.

Experts say many hate crimes go unreported and caution against drawing conclusions from such data, which have small sample sizes.

Trump has proposed building a wall on the southern border with Mexico to stop illegal immigrants and a temporary ban on all Muslims entering the country, a proposal he later scaled back.

By highlighting issues such as race, religion and national origin, the presidential election campaign could have influenced both the number of incidents and frequency of reporting them to police, Levin said.

“That, coupled with significant coverage, might have encouraged two things to happen: Individuals who vary in motivation, from hardcore bigots to those just seeking a thrill, seeking something to do, as well as victims who felt that they should report this because they’re not alone,” Levin said.

Even so, Levin said: “I don’t think we can just explain away the increase with increased reporting”.