LIMESTONE – A bomb threat shortly after the school day began forced Limestone Community School to evacuate its students Monday.

Limestone Police Chief Stacey Mahan said Monday afternoon that investigators could not yet disclose how the threat, which was received at approximately 9:30 a.m., was delivered.

Students and staff at the kindergarten through 12th grade school were taken to Veterans Memorial Gym near the High Street school.

Along with the police, the Limestone Fire Department, the Aroostook County Sheriff’s Department, and Maine State Police Trooper Shawn Whalen and his bomb-sniffing dog, Bailey, responded to the call.

Whalen and the dog searched the building and found nothing, according to Mahan.

Students returned to classes a few hours later, said the chief.

The incident remains under investigation.