MEXICO CITY, Feb 4 (Reuters) - A deadly blast that killed at least 37 people at Mexican state oil monopoly Pemex's headquarters in Mexico City was caused by a build up of gas, the government said on Monday. Attorney General Jesus Murillo said no trace of explosives was found at the site of the explosion, the latest in a string of safety lapses to hit the oil monopoly. New President Enrique Pena Nieto is seeking to push through a major overhaul of Pemex. (Reporting by Lorena Segura; Writing by Simon Gardner; Editing by Dave Graham)

By Michael O'Boyle MEXICO CITY, Feb 3 (Reuters) - Mexican rescue workers found three more bodies over the weekend amid the rubble of a deadly blast that tore through state oil firm Pemex's main office complex, the government said, as search efforts appeared to near a close. The death toll from Thursday's explosion stands at 36, Pemex said via Twitter. Rescue workers had been digging through the last sections of the building's basement and could soon call off their search. One person was reported still missing.

A blast that killed 33 people at the headquarters of Mexico's state-owned oil firm Pemex appears to have been an accident, the firm's chief said Friday as rescuers wrapped up a grueling search for survivors. Hundreds of firefighters, police and soldiers aided by dogs dug through rubble for almost 24 hours straight after the explosion ripped through an annex of the 54-floor tower in the heart of Mexico City, injuring 121 people.

Rescuers dug through mounds of rubble for survivors on Friday after 32 people were killed in a mysterious explosion at the headquarters of Mexico's state-owned oil giant Pemex. Hundreds of firefighters, police and soldiers aided by dogs have toiled since the blast ripped through an annex of the 54-floor tower on Thursday, injuring 121 people and leaving concrete, computers and office furniture strewn on the ground.