Three Turkish soldiers and eight members of the Kurdish Workers' Party (PKK) militant group were killed in clashes, the media reported on Thursday.
The clashes took place on Wednesday when the security forces carried out an operation in Mardin province, sources said.
Turkey's southeast region has seen the worst violence since a cease-fire between the government and the PKK collapsed in July 2015, Xinhua news agency reported.
Since then, more than 260 members of the Turkish security forces and thousands of PKK members have been killed.