The Flathead County sheriff says two 9-year-old boys told deputies they set fire to a semi-trailer truck hoping to see it explode.

The boys piled paper around the truck, poured gasoline on the truck and the kindling and set it ablaze with a bottle rocket, Sheriff Mike Meehan said.

The sheriff said Wednesday the truck was a total loss. He estimated the value of the 1996 Kenworth at about $30,000.

The fire was reported at about 2:30 p.m. Tuesday.

The truck was owned by Mild Fence Co. of Kalispell and was parked outside the driver's home just south of Columbia Falls, Meehan said.

The fire is still under investigation and the boys are in their parents' custody, the sheriff said.