Turkey has sent hundreds of troops into northern Iraq to chase fighters from the Kurdistan Workers' Party (PKK) in an operation likely to increase tensions within the region.
The soldiers killed four fighters escaping after a failed attack on a Turkish unit near the border, Turkey's military said.
The army did not say when their troops would withdraw, saying the soldiers were remaining in northern Iraq, supported by Turkish warplanes.
The Kurdistan regional goverment in northern Iraq has condemned similar cross-border attacks in the past, saying they violate Iraq's sovereignty.
Clashes between the PKK and the Turkish army, which started late on Tuesday, broke out in the Uludere district of Turkey's Sirnak province, near the border with Iraq, and lasted through the night.
The fighting also left a Turkish sergeant dead, Turkish security sources said.
The sources added that PKK fighters had attacked a convoy of trucks that belonged to a private construction company in the southeastern Turkish province of Hakkari.
The incident on Tuesday night took place near a military post on the border with Iraq.
The PKK were said to have released the drivers and set fire to the trucks.
Fighting has escalated in the southeast of Turkey, which is predominantly Kurdish, in recent weeks.
It follows increased infiltration by PKK members into Turkey from the mountains of northern Iraq where thousands of the fighters are based.
The PKK, which seeks an independent state for Kurds, has called off a year-old unilateral ceasefire and has resumed attacks on Turkish forces.
The group accuses the military of offensive attacks and the government of impeding a political resolution of the conflict.
More than 40,000 people, mostly Kurds, have been killed in violence since the PKK launched its armed struggle against the Turkish state in 1984.