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Some 65 people have been charged in connection with peddling horse meat unfit for human consumption, according to the European police agency Europol.

Investigators looking into "unusual behavior" in horse meat markets are said to have uncovered an operation run by an organized crime syndicate in Spain in which old and neglected horses were slaughtered and sold as meat abroad.

As part of Operation Gazel by Spain's Guardia Civil, two slaughterhouses were found to be producing horse meat "not suitable for consumption".

A total of 66 individuals were investigated in the year-long sting and now Europol has confirmed that 65 people have been charged with crimes such as "animal abuse, document forgery, perverting the course of justice, crimes against public health [and] money laundering."

The arrests were focused around the cities of Alicante and León.

"Three officers from Europol supported the Spanish actions in Alicante and León. As a result of all of these actions, several bank accounts and properties were blocked or seized, and five luxury cars seized," a Europol statement read.

In 2013, a study by the Food Safety Authority of Ireland uncovered a scam in which the presence of equine meat was being concealed in beef products.

Mislabelled meat products were subsequently discovered in a number of European countries including France, the UK and Sweden.

Dutch businessman Willy Selten was jailed in 2015 for his part in the scandal.