MEXICO CITY (AFP) - Mexican authorities have found four new mass graves in the investigation into the disappearance of 43 students, but the number of bodies in the pits is unknown, the attorney-general said Thursday.

Four new suspects took investigators to the site of the pits, where "they say there are remains of students," near the city of Iguala, 200km south of Mexico City, said Attorney-General Jesus Murillo Karam.

The four clandestine graves are "relatively" close to the location of another mass grave found last weekend that contained 28 unidentified bodies.