ZAGREB, Croatia—A military drone that apparently flew all the way from the Ukrainian war zone over three European NATO-member states before crashing in an urban zone of the Croatian capital was armed with an explosive device, Croatia’s defense minister said Sunday.

The Soviet-made aircraft crossed Romania and Hungary before entering Croatia, slamming into a field near a student dormitory late Thursday. About 40 parked cars were damaged in the large explosion, but no one was injured.

“Traces of explosives and clues suggesting that this was not a reconnaissance aircraft were found. We found parts of an air bomb,” Croatian Defense Minister Mario Banozic said at the crash site.

He said that this further raises a question about whether the drone belonged to Russia or Ukraine.

“There are elements that indicated it could have come from both,” he said.

Air crash investigators have pulled most of the drone’s remaining parts from a large crater it created on impact, including a partly damaged black box that should reveal the drone’s flight path.

Croatian officials have criticized NATO for what they called a slow reaction to a very serious incident and called into question the readiness of the military alliance’s member states to respond to a possible attack.

NATO said the alliance’s integrated air and missile defense had tracked the object’s flight path. But Croatian officials said the country’s authorities weren’t informed and that NATO reacted only after questions were posed by journalists.

“If this situation had been detected and resolved in time in neighboring countries, we would not be here today,” Banozic said.

“We will seek answers to what happened. The defense ministers of Romania and Hungary said that day they were evaluating what happened. We are waiting for an answer,” he said.

Croatian investigators identified the unmanned aircraft that crashed in Zagreb as a Soviet-era Tu-141 that was used for reconnaissance missions in both countries in the 1980s.