The bomb found in the wreckage of the unmanned aerial vehicle (UAV) that crashed in Zagreb last week weighed up to 120 kilos and exploded under the ground, the Croatian public broadcaster said on Sunday evening, citing a high-level Defence Ministry source.

Since the UAV hit the soft ground, an explosion occurred under the ground. Had it hit the asphalt or concrete, the consequences would have been catastrophic, HTV said in its prime-time evening news programme.

The bulk of this Soviet-era military drone was pulled out of the ground on Sunday morning, and Defence Minister Mario Banozic confirmed that fragments of an aerial bomb and traces of explosive had been found in the crater, indicating that it was not a reconnaissance drone.

Military analysts disagreed, telling the media that it was not an aerial bomb but a system for the self-destruction of the equipment and data.

Brigadier Ivan Selak, a retired Croatian Air Force pilot, said he was almost certain that those were not the fragments of an aerial bomb because “had there been an explosive inside, half of the nearby student dormitory would have been blown away by the blast.”

The drone, a Soviet-made Tupolev Tu-141 Strizh, crashed near a student dorm in the Jarun district of southwest Zagreb shortly after 11 pm on Thursday, damaging about 40 cars in a nearby car park. No one was hurt.

It came from Ukraine, flying over Romania and Hungary, both NATO members, at a speed of 700 km/h at an altitude of 1,300 m, before entering Croatia’s air space and crashing down in Zagreb.