A threatening phone call that led to the closing and evacuation of the preschool at Hawaii’s largest synagogue Monday has been added to a larger probe involving threats against 20 Jewish schools and community centers across the mainland the same day and some 100 hate crimes against Jewish institutions since the beginning of 2017, officials said Tuesday.

Private security guards were posted Tuesday in the parking area of Temple Emanu-El in Nuuanu as both local and federal law enforcement officials investigated the 3 p.m. incident at the Gan Yerushalayim preschool.

Richard Field, executive director of Temple Emanu-El, said a caller who refused to identify himself demanded the evacuation of the school but wouldn’t offer any reason why.

The caller refused to say whether there was any further threat to the school or offer any religious or racial motivations for the demand. Field said the man didn’t seem especially angry, either.

“He kept saying, ‘Evacuate the school. Do you understand?’” Field said.

But the administrator kept asking questions in an attempt to keep the caller on the line. Field said he managed to have the students move to a different location and call the police on his cellphone, all while the caller was on the school’s landline for five to 10 minutes.

Honolulu Police Department officers drove up just as the caller apparently became impatient and hung up, he said.

Field said FBI agents told him the incident differed from Monday’s mainland cases because there was no threat of a bomb. However, they did say it was similar in that it may have been an internet-based call, he said.

Special Agent Arnold Laanui of the FBI Honolulu office on Tuesday would not disclose any details about Monday’s incident, but acknowledged the wider investigation of hate crimes involving synagogues, schools and Jewish cemeteries.

The New York-based Anti-Defamation League issued a security advisory to Jewish institutions across the country Monday following what they described as a “fifth wave” of bomb threats. On Monday threats were made in at least 12 states, including Alabama, Delaware, Florida, Indiana, Maryland, Michigan, New Jersey, New York, North Carolina, Pennsylvania, Rhode Island and Virginia.

“While this latest round of bomb threats to Jewish Community Centers and day schools across the country again appears to not be credible, we are nonetheless urging all Jewish institutions to review their procedures,” Anti-Defamation League CEO Jonathan A. Greenblatt said in a statement.

On Saturday hundreds of headstones were overturned at a Jewish cemetery in Philadelphia, according to reports, while a Jewish cemetery in St. Louis was vandalized earlier.

President Donald Trump brought up the issue in his speech to Congress on Tuesday night.

“Recent threats targeting Jewish community centers and vandalism of Jewish cemeteries, as well as last week’s shooting in Kansas City, remind us that while we may be a nation divided on policies, we are a country that stands united in condemning hate and evil in all of its very ugly forms,” Trump said.

Field said the young students were in good spirits and that staff members acted professionally during the incident. Several parents were “quite upset,” he said, but only four students did not return to school Tuesday.

“I’m very grateful and thankful nothing bad happened, and I’m proud of how our staff handled themselves, especially with how much stress they were under,” Field said.

He said community support has been “tremendous,” with many reaching out to express their dismay and wishing the school well. Some have even offered to pay for the security, he said.

Field said the security service will remain on the job for the immediate future.

“We are extremely thankful that no one was hurt and want to assure the members of our Temple Emanu-El and school community that we will operate in a way that puts the safety of our students, staff, visitors and premises first,” the temple posted on its Facebook page.