Minerales de Monclova told the Associated Press that an accident Friday at its La Esmeralda mine was caused by methane gas that exploded, after which a portion of the mine collapsed.

While news service Reuters initially reported late Friday that the fourth miner was assumed dead at the mine in the state of Coahuila, the AP later quoted mine management that the bodies of all of those killed had been recovered.

Labor secretary Javier Lozano confirmed the names of three of the victims for local media as Mario Alberto Flores, 34; Miguel Hernandez, 38; and Angel Gonzalez, 36.

According to Reuters, the operator of the mine is Minera del Norte, an arm of steelmaker Altos Hornos de Mexico.

There were 132 other workers underground at the time of the incident, all of whom escaped without injury, both reports said.

The fatal event is the second for the country in four months; 14 workers died May 3 at another operation in the Coahuila state.