(CNN) - Students at a Montana elementary school were evacuated on Tuesday when a homemade bomb detonated on their playground. No children were injured in the explosion, officials said.
An improvised explosive device, or IED, exploded shortly after a school official found it at Rossiter Elementary School in Helena, the Lewis and Clark County Sheriff's Office reported.
Children were quickly bussed to a nearby school to wait for their parents to pick them up. A stretch of road in front of the school remains closed for investigation, the sheriff's office said.
All Helena and East Helena schools were swept and cleared after initial lockdowns, but Rossiter remains closed indefinitely, the sheriff's office said.
Authorities aren't sure who planted the device, which they described as a soda bottle with duct tape around it, or whether there are any other devices, Sheriff Lee Dutton said in a press conference shared by CNN affiliate KRTV Tuesday morning.
"Things are under control, no one was hurt and we're taking appropriate precautions," Dutton said.
Officials are sweeping state government buildings around the capital and urge schools to stay alert as they learn more.
The FBI, Montana Highway Patrol, Helena Police Department and Bureau of Alcohol, Tobacco, Firearms and Explosives are assisting the sheriff's office in the investigation, CNN affiliate KTVH reported.
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