Serbian security forces stopped a group smuggling migrants from Bulgaria and arrested three people, the defence ministry in Belgrade said Tuesday.
A joint police and army patrol caught the gang with 64 migrants, all of them Afghan nationals, at Zajecar, close to Serbia's border with Bulgaria.
The van was packed with 34 people, among them a pregnant woman, a baby and a child. The driver previously made a run with 30 migrants, leaving them with two accomplices for further transport by cars.
All three smugglers were taken into custody and will face a judge, the statement said.
Serbia straddles the route that migrants, mostly from Asia, have taken to reach wealthy EU countries such as Germany and Sweden.
Balkan countries closed their borders to migrants in March after some 1 million people entered in about 10 months.
Under an EU-Turkey deal, refugees are now screened in Turkey, while so-called economic migrants mostly resort to traffickers and other surreptitious means to cross the sealed borders.
Around 4,500 people are presently stranded in Serbia, UN refugee agency UNHCR says.