Police in Israel say they have arrested a 19-year-old Jewish man as the primary suspect in a string of bomb threats targeting Jewish institutions in the United States.

Police spokesman Micky Rosenfeld described the man as a hacker but said his motives were unclear.

Rosenfeld told the AP that the suspect is "the guy who was behind the JCC threats," referring to Jewish community centers in the U.S. that have received dozens of anonymous threats in recent weeks.

Threats last month targeted Jewish centers in New Jersey, Pennsylvania and Delaware, including those in Cherry Hill and Wynnewood. No bombs were found, but the threats prompted evacuations, rattled nerves and caused unease.

It was not immediately clear which specific cases the suspect had been linked to.

An FBI statement said the agency and Israeli National Police "worked jointly to locate and arrest the individual suspected for threats to Jewish organizations across the United States and in other parts of the world."

The statement did not provide further specifics on the suspect or which threats he was believed tob e connected to.

The Washington Post reported that the man appeared to be behind the bulk of the threats.

The Feb. 27 evacuations at the Katz Jewish Community Center and Jewish Federation of Southern New Jersey in Cherry Hill, and the Perelman Jewish Day School (Stern Center) and the Kaiserman JCC in Wynnewood came on a day when a wave of threats were reported at similar centers in at least a dozen states. Other threats that day were called into centers in Harrisburg and York in Pennsylvania, and Wilmington, Del.

In the wake of the local threats, several peaceful rallies have been held to denounce anti-Semitism and other hateful acts, and law enforcement have increased patrols at houses of worship and other religious sites.

The man held both Israeli and American citizenship, according to Haaretz. The newspaper reported that the suspect was first linked to a 2016 bomb threat at a Jewish institution in New Zealand and then a similar incident in Australia.

Police struggled to find the suspect but received information from the FBI after the agency found that threats at 16 Jewish centers in nine U.S. states – Florida, New Jersey, Delaware, Maryland, Tennessee, Georgia, Pennsylvania, South Carolina and North Carolina – also originated in Israel, according to Haaretz.

His attorney, Galit Bash, told the news outlet that the man did not have a criminal record and suffered from "severe medical problems" that could affect "his cognitive functioning."

Rosenfeld told the AP that the suspect allegedly placed dozens of threatening phone calls to public venues, synagogues and community buildings in the United States, New Zealand and Australia. He also placed a threat to Delta Airlines, causing a flight in February 2015 to make an emergency landing.

Rosenfeld said the man, from the south of Israel, used advanced technologies to mask the origin of his calls and communications to synagogues, community buildings and public venues. He said police searched his house Thursday morning and discovered antennas and satellite equipment.

"He didn't use regular phone lines. He used different computer systems so he couldn't be backtracked," Rosenfeld said.

After an intensive investigation in cooperation with FBI representatives who arrived in Israel, as well as other police organizations from various countries, technology was used to track down the suspect who had made the threats around the world, Rosenfeld said.

"Today's arrest in Israel is the culmination of a large-scale investigation spanning multiple continents for hate crimes against Jewish communities across our country," Attorney General Jeff Sessions said in a statement. "The Department of Justice is committed to protecting the civil rights of all Americans, and we will not tolerate the targeting of any community in this country on the basis of their religious beliefs."

The Anti-Defamation League says there have been more than 150 bomb threats against U.S. Jewish community centers and day schools in the U.S. since Jan. 9. The group expressed relief at the news of the arrest.

There have also been multiple acts of vandalism at Jewish cemeteries, including Mount Carmel in Philadelphia's Wissinoming section.

In late February, about 100 toppled headstones were discovered at the burial ground. The investigation into the damaged gravestones remains underway. Fundraisers are also in progress to help fix the damage.

Nearly $220,00 has been raised thus far for the restorations, which are expected to begin next week.

This article contains information from the Associated Press.