Machinery located at three oil pipeline construction sites in central Iowa has been extensively damaged by fire.

Jasper County Sheriff John Halferty says it appears the fires were intentionally set along the Dakota Access pipeline.

Halferty says damage to bulldozers and other heavy equipment is estimated at $1 million.

The Newton Daily News reports (http://bit.ly/2apGmwK ) the sheriff's office was alerted around 6 a.m. Monday to a fire in a farm field west of Newton. Investigators later learned of additional burned equipment at pipeline sites near Reasnor and Oskaloosa.

Texas-based Dakota Access says "it's a shameful act by a group of people trying to disrupt our energy security and independence."

The pipeline, which crosses 18 Iowa counties, has received strong opposition from environmental and landowner rights groups.