The acquittals came two weeks after the court accepted a request from defence attorneys to exclude recordings they said were obtained illegally by Serbian and Slovenian police.

"Evidence gathered in Slovenia and Serbia had to be excluded, while the remaining evidence, related to alleged drug trafficking in Italy and Uruguay, was not sufficient for a sentence (against the 13 acquitted)," said Judge Gorazd Fabjancic.

The court sentenced the remaining defendants, who were detained in Italy, to between four and 10 years in prison on charges of drug production and trafficking.

Slovenian police arrested the 17 in an operation launched in 2010. The accused were accused of belonging to a gang led by Serbian national Darko Saric, an alleged drug kingpin who has been charged with trying to smuggle 2.8 tonnes of cocaine from South America to Europe but remains at large.

Among those arrested was Dragan Tosic, allegedly the head of Saric's Slovenian crime branch and the owner of two well-known Ljubljana coffee shops.

Tosic was among those acquitted Tuesday, after an 18-month trial that had been dubbed the "Balkan warrior" case.

Slovenia, the only former Yugoslav state that has joined the European Union, is located on a major drug trafficking route linking Central Asia with Western Europe.

Copyright AFP (Agence France-Presse), 2012