Mexico City (CNN) -- Workers digging through the rubble of what were offices at Mexico's state-run oil giant have found more victims, raising the death toll from last week's blast to 35.
Pemex, the oil monopoly, on Sunday confirmed the figure, which was above the 33 reported killed earlier.
More than 100 people were injured; two people remain missing.
Pemex, the powerful but much-criticized state oil company, has said it's not clear what caused the blast, which took place Thursday at an administrative building in the Pemex office complex in Mexico City.
Authorities have said investigations are under way to determine whether the explosion was the result of an accident, negligence, or an attack.
"People were screaming. ... You could see pieces of the wall falling to the ground," said Joaquin Borrell Valenzuela, an attorney for the Pemex comptroller's office, who was in a courtyard outside the building at the time of the blast.
Paramedics quickly arrived and started pulling people from the debris.
Thousands of people work at the Pemex headquarters, which includes a 54-story building that is nearly 700 feet tall. The annex where the explosion happened is adjacent to the tower.
CNN's Mauricio Torres contributed to this report.