Ambulances rushed to the scene. The area where the explosion hit is on a road between Diyarbakir and the district of Bismil, about 50 kilometers (31 miles) east, the security sources said.
Footage showed the blast left the building's concrete frame and twisted metal exposed with the windows entirely blown out and its roof partially collapsed. The explosion left a crater on the ground, Reuters reported.
Turkey's southeast has seen some of the most intense fighting in decades after a ceasefire between the Turkish state and the outlawed Kurdistan Workers Party (PKK) collapsed in July 2015. Thousands of militants, security force members and civilians have since been killed in fighting across the region.
Monday is the anniversary of autonomy-seeking PKK, designated a terrorist group by Turkey, the European Union and the United States, taking up arms against the Turkish state in 1984. More than 40,000 people have been killed in the conflict.