Turkish warplanes launched air strikes against camps of the Kurdish separatist group PKK in northern Iraq late on Thursday, the state news agency Anatolian said.
The operation began just before midnight and continued into Friday, Anatolian said.
Military sources told Reuters that at least 30 planes were bombing the area, which they said was far from civilian settlements.
The raids, expected to last several hours, were aimed against senior PKK members in the Qandil area of northern Iraq, the sources said.
Turkish air strikes inside Iraq the past week were described by Iraq as "unfortunate". Turkish troops conducted a large-scale incursion across the border in February.
Turkey blames the PKK for the death of more 40,000 people. The United States and the European Union consider the group a terrorist organisation.