(CNN) -- The headquarters of Mexico's state oil was evacuated Tuesday night -- but it turned out to be a false alarm, the company said. The Pemex Tower in Mexico City was cleared after an unspecified threat, Pemex said on its Twitter feed. A short time later, the company tweeted, "It was a false alarm." In February, a deadly explosion at Pemex headquarters killed at least 37 people. Officials said it was caused by a buildup of gas in the basement. Pemex is Mexico's powerful and much-criticized state oil monopoly. Thousands of people work at the company's headquarters, which includes a 54-story building. The annex where the February explosion happened is adjacent to the tower.
Pemex is Mexico's powerful and much-criticized state oil monopoly. An explosion at Pemex headquarters in February killed 37 people . Thousands of people work at the company's headquarters .