The 43 Mexican students who disappeared four months ago were murdered on the orders of a drug cartel who mistook them for members of a rival gang, the government said on Tuesday, finally confirming the deaths of the trainee teachers.

Their disappearance on the night of 26 September in the south-western city of Iguala led to massive street protests in Mexico and international condemnation of its security situation. It embarrassed President Enrique Pena Nieto and plunged his administration into its biggest crisis.

Until now, the government had said only that the students were almost certainly murdered after clashing in Iguala that night with corrupt police officers, who handed them over to members of local drug gang Guerreros Unidos.

"There's no doubt that the students lost their lives, their freedom and were then incinerated and thrown into the Rio San Juan," Attorney General Jesus Murillo told a news conference, referring to a river by the town of Cocula, near Iguala.

Murillo has said that the gang members suspected of killing the students had been so thorough in the destruction of their remains that it was difficult to identify them. The remains of only one of the missing students has been identified so far.

A notorious case

The mayor of Iguala and his wife were subsequently arrested as two chief suspects. The case has become notorious as an illustration of the nexus between organized crime and politics widely believed to exist across much of Mexico.

"The students were identified by the criminals as members of the rival gang in the region," said Tomas Zeron, head of the criminal investigation agency at the attorney general's office.

The office said the gangsters believed the students had been infiltrated by a gang known as Los Rojos.

Murillo dismissed the idea that the students had ties to the gang and said the investigation was continuing. He is seeking to have Rodriguez sentenced to up to 140 years in prison.

The attorney general also rejected media reports that the army could have been involved in the disappearances, saying there was not "a single piece of evidence" to back this up.