Mexico has officially confirmed the 43 students, who went missing in September, were slaughtered and incinerated in the southern state of Guerrero.

Attorney General Jesus Murillo Karam told reporters that there is "no doubt" victims were murdered, even though the investigators have confirmed the DNA identification of only one student.

"The evidence allows us to determine that the students were kidnapped, killed, burned and thrown into the river," Murillo Karam said.

Citing initial examination, the prosecutor went on: "This and many other elements provided during the investigation enabled to perform a logical casual analysis and undoubtedly reach a conclusion, that students teachers were deprived of liberty, burned and thrown into the San Juan River."

This is the first time Mexican authorities are declaring the students who disappeared earlier were killed.

He also denied the army's hand in the purported massacre as earlier alleged by some of the victims' family members.

Murillo Karam cited confessions from local gang and police personnel for the conclusion. Only one of the remains of the student have been identified by the laboratory in Innsbruck, Austria while other bodies were so badly damaged their identities could not be confirmed, the Mexican authority said.

Thomas Zeron Lucio, chief of the Criminal Investigation Agency PGR, released the excerpts from the confession of a prominent gang member Felipe Rodriguez Salgado, who goes by the nickname 'The Stubborn' or 'Brush', ordering the killing of the students.

"Students were targeted by criminals to join the antagonistic group of organised crime in the region," Lucio said saying the students were victims of mistaken identity.

The latest announcement by the Mexican authorities has come a day after thousands of protesters took to the streets in Mexico City demanding the officials to return the students. Many of them refused to accept the authorities' version and insist that the students are alive.

No less than 90 people, mostly local police officers, have been arrested since the disappearance of the students in September last year as investigators suspect mayor of the city of Iguala Jose Luis Abarca could be behind the killings.

Abarca and his wife are also in custody.