Two sappers were killed and four others wounded on Tuesday, while defusing explosives in a forest near the town of Kuznia Raciborska in southern Poland.
Two of the wounded are said to be in critical condition, according to Polish authorities.
Polish Defense Minister Mariusz Blaszczak expressed his condolences to the families of the dead military men on social media.
Kuznia Raciborska Mayor Pawel Macha told media that the area was full of explosives from the Second World War. The stash the sappers were working on neutralizing was found a few days ago.
The mayor appealed to locals not to go into the forest. In this period, it is traditional for Poles to go into the woods in search for mushrooms.