JERUSALEM -- Israeli police said they had arrested a 19-year-old Israeli Jewish man as the primary suspect in a string of bomb threats targeting Jewish community centers in the U.S.

Police spokesman Micky Rosenfeld said Thursday the suspect’s motives were unclear.

Rosenfeld said 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. He says the investigation was carried out with the help of the FBI and police from other countries. U.S. law enforcement sources confirmed the arrest and FBI involvement.

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“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 released shortly after the reports emerged. “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.”

A U.S. law enforcement official told CBS News on Thursday that the suspect is believed to be responsible for most of the threatening calls to JCC facilities and schools in the U.S. and around the world. While it is believed he’s responsible for almost all the calls, there certainly could be copycats out there still, the official said.

The FBI led the investigation, according to the U.S. official, which became international in nature when the routing of the calls was traced outside the United States. Agents believe the suspect used an anonymizer to mask his phone number and IP addresses. He may have used some kind of automation program to program calls in rapid succession at times.

Threatening calls were placed to Jewish centers across the world including in the U.S., Canada, the U.K., Australia and New Zealand.

The 19 year old is being held on charges filed in Israel. It is unclear when the U.S. might formally file charges or seek extradition.

An official with the U.S. Jewish community centers told CBS News on Wednesday that there have been 170 threats called in to Jewish institutions across the U.S. in the last 75 days.