Eight other soldiers were wounded after a homemade bomb exploded while a military convoy was passing in Uludere, close to the Iraqi border, the source said.
The bombing was blamed on militants from the Kurdistan Workers' Party (PKK) with whom the Turkish military has renewed fighting since the collapse of a two-year ceasefire in July last year.
The Turkish army's hierarchy has been badly hit in the purge since the July 15 failed coup during which a rogue military faction tried to oust President Recep Tayyip Erdogan from power.
More than 600 Turkish security force members have been killed by the PKK since the collapse of a ceasefire last year, according to a toll given by state-run Anadolu news agency on July 31.
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The government has responded with military operations against the group, killing more than 7,000 militants in Turkey and northern Iraq, the agency said. It is not possible to independently verify the toll.
Activists claim innocent civilians have also been killed in the offensives.
Over 40,000 people have been killed since the PKK first took up arms in 1984. It is proscribed as a terrorist group by Turkey, the European Union and the United States.