HARRISVILLE, Pa.—Police say there are no injuries after an apparent drive-by shooting at a Marcellus Shale natural gas drilling site in northwestern Pennsylvania.

The Butler Eagle ( http://bit.ly/hMQZ9u) reports that on Saturday a suspect in a pickup truck pointed a small-caliber rifle in the direction of a drilling rig and fired two rounds.

State police report that the occupants of the vehicle were shouting profanities at the drilling site as they fled the scene.

Authorities say there's no known motive for the shooting, nor were there any previous threats directed at the operators of the site or its employees.

Shell Exploration & Production Co., a unit of Royal Dutch Shell PLC, owns the drilling site.

Authorities are searching for leads in the case.