The aircraft is believed to have flown from the Ukrainian war zone across three countries before crashing in Croatia.
ADVERTISEMENTA military drone that crashed near Zagreb amid the war in Ukraine was armed with an explosive device, Croatian crash investigators have said.
The Soviet-era aircraft is believed to have flown all the way from the Ukrainian war zone over three European NATO member states before it was found in the Croatian capital last month.
Members of the Croatian investigative team told reporters that fragments of the drone found at the crash site showed that the device carried an “improvised aircraft bomb” filled with an unknown "explosive substance".
“It was unequivocally established that these were fragments of the OFAB 100-120 air bomb,” Major Mile Tomic said on Wednesday.
“Both the bomb and its trigger were made in the former USSR," he added.
Croatian investigators said they have not yet conclusively determined who launched the TU-141 drone -- an aircraft originally used for surveillance missions.
Both Moscow and Kyiv have denied launching it, but there are indications the drone came from Ukrainian territory.
NATO officials have refused to comment on the incident until an investigation is completed, but the alliance has stepped up surveillance flights over countries near the war zone in Ukraine.
Croatian officials have previously criticised NATO for what they called a slow reaction to a very serious incident, as well as fellow alliance members.
The six-tonne drone apparently drifted uncontrolled out of Ukraine, crossed into Romania and Hungary before entering Croatia, slamming into a field near a university campus in Zagreb.
Around 40 parked cars were damaged in the large explosion on March 10, but no one was injured.
NATO said the alliance’s integrated air and missile defence had tracked the object’s flight path, but Croatian officials said they had not been informed.