WASHINGTON — President Trump said on Tuesday that the rise of anti-Semitism in the United States since his inauguration was “horrible” and “painful,” reacting publicly for the first time to mounting threats targeting Jewish people and institutions after he drew criticism for being slow to condemn them.

During a visit to the National Museum of African-American History and Culture, Mr. Trump said he was reminded of the need to combat hatred “in all of its very ugly forms.” He spoke one day after 11 bomb threats were phoned in to Jewish community centers around the country and a Jewish cemetery in University City, Mo., was vandalized.

“The anti-Semitic threats targeting our Jewish community and community centers are horrible, and are painful, and a very sad reminder of the work that still must be done to root out hate and prejudice and evil,” Mr. Trump said.

The statement came after weeks of private complaints from leaders of major Jewish organizations to members of Mr. Trump’s inner circle, including his son-in-law, Jared Kushner, about the president’s seeming unwillingness to speak out forcefully against anti-Semitic acts. His failure to do so stoked concern among some Jewish leaders that Mr. Trump, whose presidential campaign drew the support of racist and anti-Semitic groups including the Ku Klux Klan, was at best willing to stay silent about such actions and at worst quietly condoning them.