LA PAZ, Feb. 14 (Xinhua) -- The detonation of three kilos of dynamite caused an explosion on Tuesday night in the Bolivian city of Oruro, leaving four dead and over 10 injured, the police announced on Wednesday.

The commander of the Bolivian police, Faustino Mendoza, told a press conference that the type of explosive used had been discovered and that the investigation was underway to find out who was responsible and their motives.

The explosion came 72 hours after a gas tank exploded on Sunday close to the same spot, killing 12 and injuring over 50.

"We are continuing the investigations to discover the causes of this event which left four people dead," said Mendoza.

According to the police report, the explosion killed two adults and two children, aged 4 and 8.

Mendoza added that fragments of the detonator were found, with the explosion having gouged a hole close to half a meter deep in the ground.

He added that three men had been arrested, although their involvement in the explosion has not been confirmed.

The Bolivian police has deployed a security net around Oruro and its outskirts, controlling both people and vehicles.