The incident occurred around 1700 hours on Sunday while the boy, identified as Josip Nenadovic, was playing in a wood owned by his family.
Branimir Miljevic, investigating judge of the Pozega County Court, told Hina on Monday that the boy had most probably gone to the wood to cut a fishing rod. He tripped a land mine, suffering serious injuries to the legs, and most probably died from haemorrhage.
The boy was reported missing around 2100 hours when the local police, fire brigade and residents mounted a search. His body was found nearly four hours later.
The body was transferred to the County Hospital in the nearby town of Pakrac for autopsy.
A line of separation between warring Croatian and rebel Serb forces ran in the area in the 1990s.