He said bomb experts were investigating the incident, but cautioned that it was too early to conclude it was a bomb attack against the building.
The police chief said it was possibilie that waste materials in the rubbish-collecting truck might have exploded.
Witnesses said explosives were hurled from behind trees in the cemetery, located behind the municipal building and two people on a motorbike were seen fleeing the scene.
The explosions shattered the windows of the building and damaged vehicles in the car park.
CNN-Turk and NTV, two private television stations, said the explosions were caused by mortars that were fired from the cemetery and that had fallen short of their intended target, a nearby military barracks.
Two bombs, blamed on separatist Kurdish fighters, struck a crowded street in Istanbul's European side on July 27, killing 17 people and leaving about 150 others injured.
Eight people accused of belonging to the Kurdistan Workers' Party (PKK) were subsequently arrested in connection with the blasts.
Leftist and Muslim fighters have in the past also carried out bomb attacks in Turkey's biggest city.