CUAUTITLAN, Mexico - A freight train slammed into a passenger bus and dragged it down the tracks in central Mexico on Thursday, killing 22 people and injuring 14, police said.

The bus was practically flattened by the force of the impact at a railroad crossing in the city of Cuautitlan, just north of Mexico City. Some of the bodies were so badly mangled that establishing their identities was proving difficult.

"Eleven bodies at the morgue ... have not yet been identified, and it has been difficult to determine their description and their gender, because some are unrecognizable and mutilated," the state attorney general's office in Mexico State - which borders Mexico City _ said in a statement.

The Mexico State government said 14 people were injured, many in serious condition, and that one other injured person had died at a specialized emergency hospital, bringing the death toll to 22.

It remained unclear exactly how the collision occurred.

State prosecutors said in a news release that the driver of the bus tried to beat the train at a crossing.

But an assistant state prosecutor in Cuautitlan, Alejandro Jardon, told the government news agency Notimex that investigations indicated the bus had stalled as it crossed the tracks, and the driver _ unable to restart it - fled as the train approached, leaving passengers to their fate.

The driver was detained two blocks away, shaken but unharmed. The vehicle was operated by a private bus company known as Autotransportes Mexico-Melchor Ocampo SA, according to state prosecutors.

Authorities said the train was pulling 36 empty wagons at the time. The driver and the train conductor were detained for questioning.