The police operation was conducted after a gunfire clash last Friday morning between rival migrant groups in the north of Serbia at the border with Hungary, which left three people dead and one injured.

Following the incident, Serbian President Aleksandar Vucic warned that military units might be sent to the north of the country to safeguard the security of the local population.

"It is unacceptable that the Serbian territory be used to settle scores between rival groups," Vucic said.

Firearms and drugs confiscated

The police operation on Saturday concerned the areas of Subotica, Kikinda, and Sombor - in the north near the border with Hungary and Croatia - and Pirot in the southeast, not far from the Bulgarian border.

During the searches, a number of firearms, ammunition, and drugs were confiscated, in addition to 28 cell phones. A total of 11,200 vehicles and 15,000 people were searched.

Hundreds of police took part in the operation, supported by the border guards, special forces, and anti-terrorism units.

Serbia is one of the countries on the so-called Balkan route, the path taken by thousands of migrants and refugees from Central Asia and the Middle East on their way to the Western countries of the European Union.