The blast occurred in the Silopi district, near the borders with Iraq and Syria, while the vehicle was carrying fuel to be used by workers involved in road construction, the Sirnak governor's office said in a statement.
It said the explosives were planted and detonated by members of the Kurdistan Workers Party (PKK).
The PKK, designated a terrorist group by Turkey, the United States and European Union, took up arms against the Turkish state in 1984. More than 40,000 people have been killed in the conflict, focused in southeast Turkey.
Ankara regularly targets PKK militants, both in its mainly Kurdish southeast and in northern Iraq, where the group is based. On Tuesday, Turkey launched a new operation against PKK targets in northern Iraq, as warplanes carried out air strikes on militant positions.