US Jewish organizations warned on Thursday that antisemitism remains a problem and the community should not let its guard down after a suspect in Israel was arrested for recent bomb threats.

The suspect, an 18-year-old dual American-Israeli citizen living in Ashkelon, is thought to have made threats to Jewish communities in the US, Europe, Australia and New Zealand for about the past six months.

He is believed to have generated most of the more than 100 bomb threats called in to Jewish community centers and other Jewish organizations in the United States over the past months.

Israeli police collaborated with the FBI in the arrest. A months-long investigation revealed that the man used advanced technologies to hide his identity.

Anti-Defamation League CEO Jonathan Greenblatt said the ADL was affected by the threats and is relieved and grateful for law enforcement officials who “made this investigation the highest priority.”

“While the details of this crime remain unclear, the impact of this individual’s actions is crystal clear: these were acts of antisemitism,” he said. “These threats targeted Jewish institutions, were calculated to sow fear and anxiety and put the entire Jewish community on high alert.”

Even after the arrest, Greenblatt maintains that antisemitism in the US “remains a very serious concern.”

“No arrests have been made in three cemetery desecrations or a series of other antisemitic incidents involving swastika graffiti and hate fliers,” he pointed out. “JCCs and other institutions should not relax security measures or become less vigilant.”

“It was heartbreaking to learn that a Jewish man is a prime suspect,” Jerry Silverman, president and CEO of the Jewish Federations of North America, said in a statement. “As a community and a society, we must remain vigilant in our effort to counter antisemitism and other hate crimes as they appear.”

Malcolm Hoenlein, executive vice president of the Conference of Presidents of Major Jewish Organizations, also said he hopes the increased attention to security would not be lessened now.

“In general, we should not diminish our focus,” he told The Jerusalem Post. “That’s the danger this poses: not just the threat at the time, but that people won’t take the ongoing concerns seriously.”

However, he does not think the bomb threats made by the suspect could be classified as antisemitism.

“I think it’s too hard to say this is an antisemitic incident, certainly not in the traditional sense,” he said.

Throughout the past few months, multiple Jewish organizations have said they believed the waves of antisemitism were one of the results of President Donald Trump’s campaign rhetoric and his failure to condemn such manifestations more promptly.

After the arrest, which Hoenlein said was “of course, uncomfortable,” he pointed out that the increase in antisemitic incidents began long before the election.

“The election still exacerbated tensions within the society,” he said. “There is a divisiveness that rose out of the election and that affects everybody, not just Jews.”

Trump was criticized last month for suggesting the threats that affected Jewish institutions could have been false flags designed to “make others look bad.”

“I don’t think he meant that the Jewish community was doing it to itself,” Hoenlein said. “He may have meant that it’s not antisemitism, that it could be a hoax, it could be something else. But the fact is, at that point nobody knew. Still, the federal agencies did take it seriously and did respond to it appropriately.

“Nobody can dispute the resources that were devoted to it: the FBI, the Department of Homeland Security, police departments and many others,” he added. “That is really the key test of the society: how law enforcement people respond to it.”

The JCC Association of North America, which received more than 100 threats in recent weeks, said it was “troubled to learn that the individual suspected of making these threats against Jewish community centers, which play a central role in the Jewish community, as well as serve as inclusive and welcoming places for all, is reportedly Jewish.”

The association declined to comment on whether or not it still considers the incidents part of an antisemitic wave, but said that throughout the period of concern and disruption, JCCs had the opportunity to strengthen their security protocols and procedures.

“We are confident that JCCs are safer today than ever before,” the organization said.