Workers and residents of Gurkovo blocked the Republic Pass for nearly 30 minutes today to protest the detention of Kolyo Atanasov, owner of the Bulmetal metal packaging plant.

The protest began spontaneously outside the company's production site in the town at the foot of the Balkan Mountains. Atanasov's wife and their four children joined it. The protesters want officials to say where he is now and what he is accused of.

Bulmetal is the biggest employer in the municipality, with hundreds of people working at the plant.

Police detained Atanasov late last night for up to 24 hours and took him to Sofia. The detention was part of a joint operation by the organised crime directorate (GDBOP) and the Sofia police (SDVR). SDVR said four people were detained in Gurkovo in all.

Police spent hours searching the plant and the businessman's home and seizing items. They were looking for tracking devices suspected of being used for unauthorised surveillance. SDVR said pre-trial proceedings were opened over holding or using special technical devices for covert information gathering without permission.

The prosecutor's office and the Interior Ministry have not said whether the devices were found or whether Atanasov has been charged. His detention period is still running.