MEXICO CITY (AFP) - The parents of 43 Mexican students who disappeared last year met with President Enrique Pena Nieto on Thursday to demand that authorities solve a case that has bedeviled his administration.

The parents arrived for the meeting in a Mexico City museum some 18 hours into a 43-hour fast that they launched ahead of Saturday's first anniversary of the mass disappearance.

It was only the second meeting between the parents and Pena Nieto since last year's tragedy, which has turned into the biggest crisis of his administration and caused his approval rating to dip.

They last met in October.

"We expect very little from this meeting because we know that the commitments that are signed are not honored. But we don't have another choice," Felipe de la Cruz, the spokesman for the parents, told AFP before the talks.

The students, from a rural teacher college in the southern state of Guerrero, disappeared after they were attacked by local police in the city of Iguala on Sept 26, 2014.

Prosecutors say police then delivered the young men - who had hijacked buses to travel to a protest elsewhere - to the Guerreros Unidos drug gang, which killed them and incinerated their bodies after confusing them with rivals.

But the official investigation was questioned earlier this month by independent experts from the Inter-American Commission on Human Rights (IACHR), who said there was no evidence that the students were burned in a funeral pyre at a garbage dump.

De la Cruz said the parents would ask Pena Nieto that their sons be found alive, that the army be investigated for any possible role in the case, and that the commission experts be allowed to stay in Mexico until the case is solved.

Some 120 people were invited to the closed-door meeting, including the IACHR experts, government officials, human rights organizations and other students from the Ayotzinapa teacher college.

The deputy interior minister for human rights, Roberto Campa, said he expected the meeting to be "productive" but "complicated" as it involves the sensitive issue of Mexico's thousands of disappeared.

The government and the parents were expected to hold separate news conference afterward.