Serbian authoritiers found 56 irregular migrants hidden in two vans in the eastern part of the country near the border with Bulgaria, the Associated Press reported on Thursday.

Four suspected people smugglers were detained by Serbian police.

Police found 33 of the migrants in a van traveling on a road near the border, while the remaining 23 were found in another van near the town of Bor, in eastern Serbia, according to the AP.

Irregular migrants and refugees have increasingly used the route from Turkey via Bulgaria to Serbia to reach the wealthier nations in the EU such as Germany and Sweden after the so-called Western Balkan route leading from Greece via Macedonia and Serbia to Hungary and Croatia was closed in March.