The soldiers were killed as they patrolled an area on Monday in Batman province's Gercus district in the mainly Kurdish southeast, scene of civil strife in the 1980s and 1990s that claimed more than 30,000 lives, most of them Kurds.
"A large-scale investigation is under way; we are looking into who placed the mine," a security official said.
Turkey has in the past accused Kurdistan Workers Party (PKK) separatists of planting landmines in the region.
In December five soldiers were killed in a mine blast in the southeast.
Stretches of Turkey's borders with Syria and Greece are also peppered with landmines, and hundreds of people have been killed in explosions. Many more have been crippled or wounded.
Ankara is not yet a signatory to the 1997 Ottawa Convention banning mines but has said it intends to sign the treaty.