(CNN) Police in Spain have arrested 12 members of a crime ring which smuggled cocaine-infused plastic products from Colombia before extracting the drug at three specialized laboratories.

The gang, led by grandparents and parents of the same family, was capable of producing more than 600 kilograms of cocaine each month, the national police force said in a statement

The ring shipped in plastic pellets impregnated with cocaine: a method that meant the drug was completely undetectable during standard customs checks, police explained.

Police also detained three specialists in extracting the narcotic, who had been flown in from Colombia and worked for 10 days straight without leaving the labs, according to the statement.

The operation was the result of an investigation which started in late 2018 and constituted "the biggest blow" against cocaine handling and extraction in Spain, the force said.

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