A military drone that apparently flew all the way from the Ukrainian war zone over three European NATO member states before crashing in the Croatian capital was armed with an explosive device, Croatian crash investigators said Wednesday.

The 6-ton Soviet-era aircraft apparently drifted uncontrolled out of Ukraine, crossed into Romania and Hungary before entering Croatia, slamming into a field near a student dormitory early morning on March 10 in Zagreb. About 40 parked cars were damaged in the large explosion, but no one was injured.

Members of the Croatian investigative team told reporters Wednesday that fragments of the drone found at the crash site showed that the device carried an "improvised aircraft bomb” that was filled with unknown type of explosives.

“It was unequivocally established that these were fragments of the OFAB 100-120 air bomb,” said Maj. Mile Tomic. “Both the bomb and its trigger were made in the former USSR.”

The investigators said that they have not yet conclusively determined which side in the war in Ukraine launched the TU-141 drone that was originally used in surveillance missions. But they indicated that the Ukrainians are more like to be behind the launch as “fresh” paint traces of their blue and yellow flag were found on the pieces of the wreckage that also included a red star, the Russian air force marking.

Both Russia and Ukraine have denied launching it.

NATO officials have refused to comment on the incident until an investigation is completed, but the alliance had increased its surveillance flights over countries near the war zone and a pair of US Air Force F-16s were deployed from Aviano Air Base, Italy, to Croatia on March 16, taking part in exercises and bolstering NATO’s southeastern flank.

Croatian officials had 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.

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AP writer Dusan Stojanovic contributed.