Serbia's Interior Ministry says police have arrested 15 people suspected of trafficking migrants.
Since the beginning of the year until March, the alleged criminal group is accused of smuggling more than 200 migrants from Syria, Iraq, and Pakistan across the border from Bulgaria into Serbia. Migrants were aiming to reach EU member Hungary.
Serbian authorities said the migrants were charged 1,000 euros ($1,084) for the trip.
An aspiring EU member, Serbia has promised to restrict human trafficking. It has also been accused of harassing migrants fleeing war and poverty.
The Western Balkan countries are a major gateway to Europe for migrants arriving from Africa and the Middle East.
Many migrants make the journey from the Middle East through Turkey, Greece, Macedonia, and Serbia before reaching EU and Schengen-zone member Hungary.