* 18-year-old Israeli arrested for hoax bomb threats
* Teenager accused of targeting Jewish centres
* Defense says a "benign growth" is behind his behaviour (Adds statements from Jewish leaders, U.S. attorney general, FBI, background on threats; adds byline, NEW YORK to dateline)
By Jeffrey Heller and Joseph Ax
JERUSALEM/NEW YORK, March 23 (Reuters) - A teenager with dual Israeli-U.S. citizenship was arrested in Israel on Thursday on suspicion of making dozens of hoax bomb threats against Jewish community centers in the United States, Australia and New Zealand.
The suspect, whose identity remains sealed pursuant to a court order, is 18, Jewish and a dual U.S.-Israeli national, a police spokesman said.
The teenager's alleged motives were not immediately clear.
At a court hearing near Tel Aviv, the suspect's defense attorney, Galit Bash, said the young man has a growth in his head that causes behavioral problems. She later told Reuters he has a brain tumor, which "may affect his behavior, his ability to understand right and wrong," and said the teen's father had also been held in connection with the case.
U.S. federal authorities have been investigating a surge of threats against Jewish organizations, including more than 100 bomb threats in separate waves over the past three months targeting Jewish community centers (JCCs) in dozens of states.
The threats prompted criticism of U.S. President Donald Trump for what some Jewish groups saw as an inadequate response from his administration. He condemned the incidents in a major speech to Congress in February.
U.S. Attorney General Jeff Sessions on Thursday said the arrest reflected the government's determination to prosecute those who perpetrate hate crimes.
"... we will not tolerate the targeting of any community in this country on the basis of their religious beliefs," Sessions said in a statement.
Israeli police said the teenager is believed to be responsible for most of the threats, though the precise number was not immediately clear.
The suspect, who is accused of targeting centers in Australia and New Zealand as well as the United States, began making the calls in January using advanced masking technologies to hide his identity, police said.
Authorities also said he was responsible for a previous bomb threat against a Delta Airlines (NYSE:DAL) DAL.N flight in January 2015 at New York's John F. Kennedy International Airport.
The Federal Bureau of Investigation, which took part in the probe, confirmed the arrest but declined to offer further details.
The threats forced the evacuation of many JCCs, including some with day care and school facilities for infants and young children. Coupled with other incidents such as the desecration of Jewish cemeteries, they have stoked fears of a resurgence in anti-Semitism in the United States.
In a statement, the president of the JCC Association of North America said JCC leaders were "troubled" the teenager appears to be Jewish.
The Anti-Defamation League, which fights anti-Semitism in the United States, said the alleged perpetrator's actions mattered more than his background.
"While the details of this crime remain unclear, the impact of this individual's actions is crystal clear: these were acts of anti-Semitism," the organization said in a statement.
Bash said her client was home-schooled and incapable of holding down a job. She added he had been found medically unfit for Israel's compulsory military service.
A judge ruled that he be held for at least eight more days.
U.S. authorities previously made one other arrest in connection with the threats. Juan Thompson, a former journalist from St. Louis, is accused of making several threats to Jewish organizations while posing as an ex-girlfriend as part of a revenge plot against her.