REFILE - ADDING SOURCE FOR THIRD SENTENCE Shattered windows are seen on one side of the headquarters of state oil giant Pemex in Mexico City January 31, 2013. A powerful explosion rocked the Mexico City headquarters of state oil giant Pemex on Thursday, killing at least 14 people and injuring 100 others. The blast hit the lower floors of the downtown tower block, throwing debris into the streets and sending workers running outside. It was not yet clear what caused the explosion, and the death toll could still rise, Interior Minister Miguel Angel Osorio Chong added. REUTERS/Alejandro Dias (MEXICO - Tags: DISASTER ENERGY POLITICS BUSINESS) Published: Úno. 1, 2013, 6:19 dop.