HELENA, Mont. (AP) — Montana authorities say an improvised explosive device blew up in an elementary school playground in Helena.

Lewis and Clark County Sheriff Leo Dutton told The Associated Press that nobody was injured when the explosive detonated at the Rossiter Elementary school playground.

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Dutton says no threat was made against the school prior to the explosion and authorities are investigating. It was not immediately clear if the explosion damaged any property.

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Students are being evacuated from the school after authorities made sure the path was clear of other devices.

All schools in Helena and East Helena are locked down and are being searched by officers.

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The FBI, the Bureau of Alcohol, Tobacco, Firearms and Explosives and the Montana Highway Patrol are assisting sheriff’s and Helena police officials in the investigation