The number of confirmed dead from a collision between a passenger bus and a freight train in northern Mexico has been raised to 20, officials said Saturday.

Authorities in the state of Nuevo Leon said 16 dead were taken to facilities there after Friday's crash, and officials in neighboring Tamaulipas said four fatalities were at a hospital in that state.

The cause of the accident at a grade crossing was still under investigation. It happened in the Tamaulipas town of Anahuac, which is near the border city of Nuevo Laredo, across from Laredo, Texas.

The train was operated by the Transporte Frontera line on a route from Nuevo Laredo to the neighboring state of Coahuila. Officials said the bus was traveling from Nuevo Laredo toward Nueva Rosita in Coahuila.