Migrants who were caught close to the Serbia-Hungary border are guarded by Serbian special forces near the city of Subotica on September 12.
Serbia is on the main route for migrants from Asia, Africa, and the Middle East aiming to reach the EU. Serbian police have long been at the border but have now reinforced the area with more heavily armed personnel.
Weapons were found near the makeshift migrants camp.
The deputy director of the Serbian police, Dragan Vasiljevic, said his forces were focused on keeping migrants in reception centers and keeping conflicts among them to a minimum.
Police said they detained 371 migrants along the border on September 12, including a family with two children.
According to the Serbian NGO the Asylum Protection Center, some 1,500 migrants attempt to cross into Hungary every day, and many hand over cash to people smugglers to do so.
Around half, according to Rados Djurovic of the Asylum Protection Center, were "illegally" driven back across the border by Hungarian officials.
Detained migrants sit on their knees with hands cuffed near their makeshift camp close to the border.
"Then, these individuals once more fall into the clutches of smugglers who again demand payment," he said, adding that different criminal groups were involved in smuggling migrants and engaged in violence against one another.
"We have seen a rising number of armed incidents involving migrants," Djurovic said, adding that the incidents involved various criminal groups "fighting for territory."
According to official figures, there are some 3,326 migrants in Serbian government reception centers, but many are not accommodated in such facilities and can be seen on the streets of the capital, Belgrade, and also along the border with Hungary.
Belgrade has reinforced its border with Hungary as hundreds of migrants per day attempt to cross into the European Union, amid alleged turf wars by criminal gangs and ongoing conflicts between migrants.