* Explosion kills 32, traps many, injures more than 100
* President courting private investment for state monopoly
* Pemex a byword in Mexico for accidents and oil theft (Updates with higher death toll, comments from CEO)
By Dave Graham
MEXICO CITY, Feb 1 (Reuters) - The death toll from an explosion at the Mexico City headquarters of Mexican state oil company Pemex has risen to 32, but the cause of the incident is still unclear, the company said on Friday.
Scenes of confusion and chaos after the explosion at the downtown tower, which also injured more than 100, dealt another blow to Pemex's image as Mexico's new president courts outside investment for the 75-year-old monopoly.
Pemex's chief executive officer, Emilio Lozoya, said the number of dead from the explosion now stood at 32, up from 25 overnight. It was still too early to say what had caused the blast, Lozoya told a news conference.
"A fatal incident like yesterday's cannot be explained in two hours, we are working with the best teams in Mexico and from overseas, we will not speculate," he said.
Pemex, a symbol of Mexican self-sufficiency as well as a byword in Mexico for security glitches, oil theft and frequent accidents, has been hamstrung by inefficiency, union corruption and a series of safety failures costing hundreds of lives.
Search and rescue workers picked through debris, and investigators sifted through shattered glass and concrete at the base of the building to try to find what caused the blast. It was not clear how many might still be trapped inside.
A government official, speaking on condition of anonymity, said a preliminary line of inquiry suggested a gas boiler had blown up in a Pemex building just to the side of the main tower. However, he stressed nothing had been determined for sure.
Lozoya said the four floors worst affected by the explosion normally had about 200 to 250 people working on them. That compared with about 10,000 staff in the entire complex.
The blast at the more than 50-storey skyscraper that houses administrative offices followed a September fire at a Pemex gas facility near the northern city of Reynosa which killed 30 people. More than 300 were killed when a Pemex natural gas plant on the outskirts of Mexico City blew up in 1984. (Editing by Louise Ireland and Vicki Allen)