Three people died and 17 were injured in Brazil on Thursday after an explosion destroyed a restaurant in downtown Rio de Janeiro, authorities said. Sergio Simoes, chief of the fire department and Civil Defense State Secretary, told reporters the most likely cause of the explosion was a gas leak inside the File Carioca restaurant. An official at the local gas company said it had not supplied gas to the restaurant since 1961, but police and fire authorities believe the gas leak could have come from the illegal use of six gas cylinders that had been found in the rubble left after the explosion. \"It is irresponsible of whoever used this kind of gas cylinders in this kind of place,\" said Simoes, adding that gas cylinder was strictly forbidden in the building the restaurant is located. Authorities said the gas may have accumulated since Tuesday evening and through Wednesday\'s public holiday when the restaurant was closed. The explosion was caused shortly after restaurant employees returned to work earlier on Thursday and started turning on equipment, said Simoes. The restaurant was located on the ground floor of a 12-floor building. Eight floors were affected by the explosion. The entire building and neighboring buildings were under inspection by the Civil Defense Department. All three dead had been working in the restaurant at the time of the explosion. Among those injured, four are reportedly in critical condition at a nearby hospital, while others only suffered minor cuts and abrasions.