Washington, Apr 22 (IANS): A young man accused of making a series of threatening phone calls to Jewish community centres across the US earlier this year was charged in two federal complaints, officials said.

Eighteen-year-old Michael Ron David Kadar, who holds dual Israeli and US citizenship, was arrested in Israel last month but police were still trying to determine his motive at the time, CNN reported.

"This kind of behaviour is not a prank, and it isn't harmless. It's a federal crime," said Federal Bureau of Investigation (FBI) Director James Comey in a statement on Friday.

"It scares innocent people, disrupts entire communities and expends limited law enforcement resources."

The threats rattled Jewish community centres, schools and other institutions across the USs and abroad, but Kadar is specifically being charged for threats made in Florida and Georgia.

"These threats of violence instilled terror in Jewish and other communities across this country, and our investigation into these acts as possible hate crimes continues," CNN quoted Attorney General Jeff Sessions as saying.

It was not immediately clear when Kadar will make his first US court appearance or where that will take place, as he is not yet in the country.

The Anti-Defamation League welcomed the filing of criminal charges against Kadar.

"These threats were hate crimes that sparked widespread fear in these intentionally-targeted Jewish community institutions -- causing evacuations, significant service disruptions, program cancellations, and deep community anxiety," the Jewish civil rights organisation said in a statement.