Officials on Thursday said, a spill that sent massive amounts of oil into the Po River in northern Italy was a deliberate act of vandalism.

The Italian news agency ANSA has reported that investigators said someone opened a valve on an oil tank Tuesday at a former refinery near Milan. An amount of oil equivalent to the load carried by 125 tanker trucks spilled into a tributary of the Po.

The spill was described as a "criminal act" by Roberto Formigoni, the governor of Lombardy, after flying over the affected area on Thursday.

He further said," They need to find out who did this and apply the harshest penalties possible."

Though with limited results, cleanup teams have been using floating barriers to slow the progress of the oil slick. The oil has reached the Po on Wednesday and is expected within three or four days to traverse the river delta near Venice and flow into the Adriatic Sea. (With Input from Agencies)