Police in Bulgaria have detained former prime minister Boyko Borisov as part of an investigation into alleged blackmail dating back to 2014-2019, prosecutors said on Friday.

Former finance minister Vladislav Goranov was also detained late on Thursday for 24 hours, prosecutors said in a statement.

The interior ministry said on Thursday the arrests were part of an operation linked to some 120 investigations by the European Public Prosecutor's Office (EPPO), which investigates large-scale fraud with EU funds, in Bulgaria. 

However, prosecutors said that the fact that police had informed them of the blackmail allegations and the detentions suggested the case did not come under the mandate of EPPO.

Sofia City Prosecutors will have to decide later on Friday whether to extend Borisov's detention to 72 hours or release him, after examining the details of the investigation, they said.

Borisov has repeatedly denied any wrongdoing to different allegations of graft-prone activities in the past decade.

(With input from Reuters)