An Israeli-American teenager was charged in separate complaints on Friday for making hundreds of hoax bomb threats to Jewish community centres in Florida and Georgia.

Michael Ron David Kadar, 18, who has dual citizenship and lives in Israel, made at least 245 threatening telephone calls between 4 January and 7 March, with a significant portion of them targeting Jewish community centres in the United States, according to the Florida complaint.

Kadar also is responsible for more than 240 hoax threats called into schools across the US and Canada between August and December 2015, forcing thousands of students to be evacuated, according to the Georgia complaint. He had not previously been linked to those calls.

Kadar, who is Jewish, was arrested in Israel on 23 March by Israeli national police and has remained in custody there. Israeli authorities had withheld his name pending a formal indictment.

US and Israeli authorities have not publicly offered a possible motive. Kadar's defence lawyers in Israel have said he was home-schooled and suffers from a growth in his head that causes behavioural problems.

The US Justice Department did not say whether it would seek his extradition.

"This kind of behavior is not a prank, and it isn't harmless. It's a federal crime," FBI director James Comey said. "It scares innocent people, disrupts entire communities and expends limited law enforcement resources."

The waves of threats against Jewish groups forced widespread evacuations, including of centres with young children, and prompted concern among Jewish leaders about a resurgence of anti-Semitism. Israeli authorities have said the calls also went to institutions in Australia, New Zealand and Canada.

The complaints against Kadar provided new detail about the evidence authorities have, including a flash drive found in his laptop containing recordings of numerous telephoned threats and media reports about those calls.

Kadar spontaneously told officers who arrested him at his house in Ashkelon, Israel, that he "did not do it," according to the Florida complaint. When asked what he meant, he referred to the Jewish community centre threats, even though no officer had mentioned them, the complaint said.

Kadar also has a speech impediment that matched one observed in recordings of the threat calls, US authorities said.

It was not immediately clear why charges were brought only in Florida and Georgia, after Jewish community centres in dozens of states were hit by the threats Kadar is accused of making.