Earlier, chief prosecutor Sotir Tsatsarov told public BNR radio that those detained were "all customs officers from the morning shift, who control the entries into Bulgaria at the Kapitan Andreevo" border checkpoint.
More than 100,000 leva (50,000 euros, $55,000) was found in a hundred raids in five towns close to the border, Popova said.
The officers allegedly would let vehicles drive past without being searched, in exchange for five to 300 euros each, prosecutors said.
Prime Minister Boiko Borissov said he expected up to 100 people to be taken in for questioning as part of the probe.
Kapitan Andreevo is the largest and busiest border checkpoint in the Balkans and a major crossing point on the route between Europe and the Middle East.
By Sunday afternoon, it was reopened after a queue a dozen kilometres long of trucks, waiting to enter Bulgaria, had formed the Turkish side.
Bulgaria`s position at the European Union`s exterior border makes it a major crossroads on the route of smugglers and human traffickers.
Migrants are regularly caught at Kapitan Andreevo trying to cross into Europe hidden inside trucks.
Cigarette smuggling is another lucrative business with a major ring dismantled last March.
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