Mexican authorities on Monday stood by their conclusion that 43 students who disappeared last year were incinerated at a landfill by a drug gang, even though independent investigators rejected that account.

Tomas Zeron, the director of investigations at the attorney general's office, told Radio Formula that "conclusive" expert analyses show that "a great number of students were executed at the garbage dump, incinerated and then (their remains) taken to a river."

Zeron spoke a day after investigators from the Inter-American Commission on Human Rights released a report saying that there was "no evidence" that the young men were burned at that site.

Attorney General Arely Gomez said on Sunday that her office would take the commission's report into account and she ordered a new forensic investigations at the dump site.

Zeron said the new forensic investigation would "attempt to reach a unanimous decision about what happened there and validate our (conclusion)."

The commission cited an international fire expert who concluded that it would take 60 hours and nearly 60 tonnes of wood, tires and diesel to cremate 43 bodies.

Citing the testimony of gang suspects, the attorney general's office had declared last year that the students had been incinerated in a huge funeral pyre that lasted 14 hours.