Two men were killed, and two others injured, in a natural gas explosion in a rural area near Nachusa on Tuesday.

The explosion appears to have occurred after the natural gas pipeline was struck by a tractor.

The two men killed have been identified as Rory Miller, 59, and his 30-year-old son, Ryan Miller. Both men were farming in a field when the explosion occurred.

Two other men were injured. One of them, 20-year-old Michael Koster, remains hospitalized with critical injuries. The other, who was not identified, has been released from the hospital.

Official causes of death have not been released for the two men killed, and the collision remains under investigation.