The blast occurred in the early afternoon on Tuesday as the soldiers were defusing an unexploded munition that had been discovered three days earlier.
"The forest is full of unexploded ordnance. It has been a problem for this place since the war," PAP was told by Kuznia Raciborska mayor, Pawel Macha.
Earlier, it was reported that six soldiers were injured in the blast, including one seriously.
The two seriously injured sappers underwent operations and complex diagnostics in hospitals in the nearby cities of Katowice and Sosnowiec and had sustained serious injuries to their faces and skulls, according to hospital officials.
The other two injured soldiers were in a non-life-threatening condition, and one of them is said to have left the hospital already.
The explosion area has been cordoned off by the army. (PAP)