The death comes after four Turkish troops died yesterday in what the army said was an air strike in northern Syria by the forces of President Bashar al-Assad.
Seventeen Turkish soldiers have been killed since the military began an unprecedented operation there on August 24 to back pro-Ankara rebels.
Turkish planes also carried out air strikes against seven IS targets in northern Syria, the army said in a statement carried by the state-run Anadolu news agency.
Yesterday's casualties died in an air strike "assessed" to have been carried out by Syrian government forces, the army said, in the first time it has blamed the Assad regime for a deadly strike on its troops.
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Three were killed at the scene, while the fourth died of his wounds in hospital, Dogan news agency said.
Turkey launched the operation in August -- dubbed "Euphrates Shield" -- in support of Syrian rebel fighters seeking to retake IS-held territory in northern Syria and also to halt the advance of Kurdish militia.
They are now pressing to take Al Bab from the jihadists and will then move to Manbij to ensure there are no Kurdish militia members remaining, as agreed with Washington.
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