MADRID, Spain — Spanish authorities have confiscated 11 metric tons of cocaine and arrested 20 people in two different operations against the smuggling of the illegal drugs inside shipping containers, Spain’s National Police said Tuesday.

Police said that 7,500 kilograms of cocaine seized by agents in the northwestern city of Vigo were hidden between pieces of frozen tuna. Investigators said that a criminal organization was using a frozen seafood company as a front to bring the drugs from South America to Spain.

A separate sting by police in the Mediterranean city of Valencia led to the seizure of 3,400 kilograms of cocaine found in false bottoms of shipping containers in the eastern city’s port.

Police didn’t reveal the exact dates of the operation, only indicating that they had been carried out recently. They said both rings were linked to criminal organizations from the Balkans region.