According to the sources who spoke on condition of anonymity, the explosive was detonated while a security convoy was passing by on a highway linking the provinces of Mardin and Diyarbakir.
Ambulances rushed to area, and the highway has been closed to traffic.
The military has launched an operation to nab the assailants.
More than 1,200 people, including security force personnel and civilians, have lost their lives since the PKK -- listed as a terrorist organization by Turkey, the United States and the European Union -- resumed its decades-old armed campaign in July 2015.
Since that month, PKK attacks have left 793 security personnel martyred and 314 civilians, including women and children, dead. More than 4,000 security personnel and over 2,000 civilians have been injured.
Meanwhile, more than 10,000 PKK terrorists have been killed or apprehended in anti-terror operations. Around 5,500 weapons, 652,000 rounds of ammunition, over 142 tons of explosives, and 15,000 bombs have been seized.