Gerdau on Thursday issued a statement confirming that there was an incident and said three employees and a contractor were injured, WQAD-8 television reported. All were taken to local hospitals, and two have been treated for their injuries and released, the station said. 

Gerdau did not provide details of the incident. 

"Gerdau’s priority is attending to the injured, their families and employees at the Iowa plant," the company said in the statement. "The company has activated its employee assistance program to offer its services to the injured and their families."

Police in Wilton said the explosion occurred around 10:30 p.m. and damaged a building at the mill.