Bulgaria's prosecuting authority has indicted four with charges of running an organized criminal gang involved in drug trafficking, Deputy Chief Prosecutor Borislav Sarafov has said.

At a press conference, Sarafov said the defendants - named as Plamen Popchev, Vasil Tsvetkov, Dimitar Yulev and Anya Marinova - were allegedly involved in the gang, led by Popchev, between September 2016 and mid-March of this year.

Police announced last week that authorities had detained the members of ring that helped smuggle cocaine (instead of heroin) from Turkey into the Netherlands. The official statement then contained information about six people arrested throughout Bulgaria.

The drug was hidden in secret compartments of cars and trucks used by the defendants to bring heroin into the Netherlands. The same vehicles transported heroin and amphetamines on their way back.

Sarafov, quoted by Dnevnik.bg, described the method as "unique", given that the secret compartment had a special locking mechanism and could only be opened with a remote control.

The heroin was brought into the country by members of the gang who crossed unnoticed from Turkey carrying rucksacks.

Separately, the Interior Ministry's Drug Substances Department, its regional anti-organized crime unit in Varna, and the national agency combating organized crime (GDBOP) were awarded for that and other investigations by officials at the press conference, which was also attended by Chief Prosecutor Sotir Tsatsarov and Interior Minister Rumyana Bachvarova.