It said Yussef al-Agha died in Khan Yunis in the collapse of a “resistance tunnel,” the type dug for attacks against Israel.
Last year, 22 members of Hamas’s armed wing were killed “preparing equipment,” the majority in a string of tunnel collapses, the group said last month.
It says Hamas has since been rebuilding the network.
“Attack tunnels” were a key weapon for Hamas during the last conflict in 2014, with a number of surprise raids inside Israeli territory.
Several Palestinians were also killed last year in tunnel collapses on southern Gaza’s border with Egypt.