Attorney General Tarek Saab appointed four prosecutors to investigate the tragedy, which caused suffering to dozens of families.
"The result of preliminary inquiries suggests that 66 men and two female visitors have died," Saab said on Twitter.
In August, clashes between rioting prisoners and security forces reportedly killed 37 inmates in the southern Venezuelan state of Amazonas,
In 2016, the explosion occurred on the visiting day in jail of San Juan de los Morros, in Guarico State. At least one person was killed and 22 others were injured.