The Soviet-made aircraft, which was built in Romania and Hungary, crashed into a field close to a student dormitory on Thursday night. The explosion caused damage to 40 cars, but no injuries.
"Traces of explosives were found and clues that suggested this aircraft was not a reconnaissance plane. Mario Banozic, Croatia's Defense Minister, stated that parts of an aerial bomb were found at the crash site.
He stated that this raises the question of whether the drone belongs to Russia or Ukraine.
He said that there were elements that suggested it could have been from both.
Investigators from the Air Accident Investigations Unit have recovered most of the drone’s parts from the large impact crater. They also found a partially damaged black box which should provide information about the drone’s flight path.
Croatian officials criticised NATO's slow response to serious incidents and called into question whether the military alliance was ready to respond to an attack.
NATO claimed that the missile and integrated air defense systems of the alliance had followed the object's flight path. Officials from Croatia claim that the object's flight path was not tracked by NATO's integrated air and missile defense systems.
Banozic stated that if this situation was detected and solved in time in the neighboring countries, then we wouldn't be here today.
"We will search for answers as to what happened. Romanian and Hungarian defense ministers said they were still evaluating the events. He said, "We are still waiting for an answer."
Croatian investigators have identified the unmanned aircraft that crashed at Zagreb as a Soviet-era Tu-141, which was used in reconnaissance missions in both Croatia and the Soviet Union in the 1980s.