Police said the apprehended suspects are members of an international criminal gang which smuggled the drugs to Slovenia and other European countries, mainly Great Britain and the Netherlands.

The 12 people arrested in Slovenia are aged between 25 and 50 and mostly come from the area around the city of Celje, east, head of the Criminal Police Marjan Fank told the press on Tuesday.

The Slovenian suspects were mostly responsible for trafficking drugs for the gang and running distribution in Slovenia, the police said.

Fank said the investigation involved police forces from eight countries, including Great Britain and the Netherlands, where the suppliers and buyers were located, and transit countries Italy and Germany.

The gang trafficked and sold cocaine and amphetamines, while the bust in Great Britain on Monday uncovered more than EUR 1m in drugs. An unspecified number of people were arrested in Great Britain, with Fank saying that none were Slovenians.

Additionally, more than 10kg of drugs of unspecified value were seized in Slovenia.

Police statistics show that drug production and trafficking or at least the number of cases discovered has been on the increase in Slovenia.

While the number of cases has been rising almost consistently, from 145 in 2007 to 292 in 2012, Bojan Dobovšek of the Maribor Faculty of Criminal Justice and Security has told the STA that this could merely reflect police becoming more effective and cooperating more with colleagues from other countries.

He moreover noted that the problem with criminal organisation was that there were several of them and that "as soon as one stops one, another one fills the void".

He said that Albanian, Serbian, Montenegrin, Russian and Italian as well as other criminal groups were active in Slovenia.