Italian police said Wednesday they had disrupted a Turkish criminal operation "with terrorist purposes", arresting 19 individuals including reportedly a major boss associated with recent attacks in Turkey.

Hundreds of police carried out the arrests of the Turkish citizens in Italy, Switzerland, Germany and Turkey, police said in a statement, targeting an alleged criminal conspiracy "aimed at setting up an association with terrorist purposes and committing terrorist attacks".

The group is also suspected of murder, international drug trafficking, and aiding and abetting illegal immigration, the police statement said. 

Italian news media reported that among those arrested was Baris Boyun, 39, known as the ringleader of a gang notorious for carrying out murders in Turkey, including via a motorcycle hit squad. 

Most recently in February, the group was associated with an armed attack at an Istanbul campaign rally for a mayoral candidate from President Recep Tayyip Erdogan's ruling AKP party, ahead of local elections in Turkey.

Turkey's interior minister announced in March a major operation against the group, arresting 13 suspects in Turkey's northwest province of Tekirdag suspected of planning assassinations and armed attacks.

Another eight suspects allegedly from the group were detained in April in Izmir, according to Interior Minister Ali Yerlikaya. 

In a statement, Milan prosecutors said investigators found the criminal group in Italy was "linked to other foreign ones, scattered over the European territory" all of them "connected with each other and able to support each other logistically, above all by guaranteeing weapons, men and means of all kinds."

Italian media said Boyun had been under house arrest in Viterbo, north of Rome, having been arrested in August 2022 on an international warrant. 

An Italian court had earlier denied a request for his extradition to Turkey, news reports said.