The police arrested two men who secured the building in front of which the car with the Croatian diplomats was parked, and two of their friends.
The arrested are Aleksandar Boskovic, 24, and Goran Piljagic, 24, who secured the apartment building in front of which the incident happened, and their friends Slobodan Dragutinovic, 25, and Zoran Guberinic, 20, all from Belgrade.
Appropriate legal measures will be taken against the perpetrators in consultation with the prosecution, the ministry said.
Deputy Ambassador Branislav Loncar and first secretary Boris Herceg were attacked as they were sitting in a car with diplomatic licence plates. They were approached by a man who started throwing insults at them, which prompted Loncar to call the police. Three men came out of a nearby car with Italian licence plates and came to the diplomats' car. One of them smashed a window on the car, hitting Herceg, who was in the driver's seat and sustained light injuries.
Police arrived shortly after the incident but the attackers had fled.
Serbia and Montenegro Foreign Minister Vuk Draskovic condemned the incident in a letter to his Croatian counterpart Kolinda Grabar-Kitarovic.
The Croatian Foreign Ministry sent a protest note to Serbia and Montenegro over the assault.