Thousands of employees of Mexican state-owned oil monopoly Petroleos Mexicanos returned to work Wednesday at the company's headquarters in this capital, where an explosion last week left 37 dead and more than 100 injured.

Pemex CEO Emilio Lozoya met in the morning with the workers, who observed a minute of silence in honor of the victims while a Mexican flag flew at half-mast.

Activities resumed at the office complex except for the B1 and B2 buildings, which were hit by a powerful explosion last Thursday that investigators said was caused by an accumulation of gas.

Pemex said experts from industry and academia found the blast caused no structural damage to the 54-story Pemex Tower and four other buildings of the office complex.

An inspection of the buildings' basements using hi-tech equipment, meanwhile, confirmed there was no trace of gas in the installations.

A banner with the phrase "Pemex More United" was placed on one of the dividers used to seal off the explosion-hit area, where workers were still removing debris. EFE