By Lizbeth Diaz and Simon Gardner
MEXICO CITY (Reuters) - Pope Francis will visit some of the poorest and most violent corners of Mexico on his first visit as pontiff, and will also head to the northern border to address the plight of migrants trying to reach the United States.
More than 100,000 people have been killed in Mexico's drug wars over the last decade and its reputation was battered by the case of 43 students abducted and apparently massacred in 2014.
President Enrique Pena Nieto´s government botched the investigation, and relatives of the victims are looking to Francis for help in getting to the truth.
"The pope ... is coming to see how institutions have sought to forget the case of our children and leave it in impunity. He will see how drug gangs have infiltrated the government," said Meliton Ortega, whose son Mauricio is among the 43.
So far, the remains of just one of the students has been positively identified from charred bone fragments the government says were recovered from a garbage dump in the restive state of Guerrero in southwest Mexico.
A team of international experts probing the case has rejected the government's version of events.
Relatives of the students will be among those attending a Mass the pope will say in Ciudad Juarez, on the border with Texas, which was for several years one of the world's most violent cities.
He will also celebrate Mass with indigenous communities in Mexico's poorest state, Chiapas, speak with young people in Morelia, the capital of violence-torn Michoacan state, and visit prison inmates in Ciudad Juarez.
There is no private meeting planned between the students' relatives and the pope, although such encounters are often organized at the last minute.
Ahead of his visit, which begins on Friday, Francis urged Mexicans to battle against corruption and drug gang violence.
"The Mexico of violence, the Mexico of corruption, the Mexico of drug trafficking, the Mexico of cartels, is not the Mexico our Mother wants," the pope said in a video released by the Vatican last week, referring to Our Lady of Guadalupe, who Roman Catholics venerate as the patroness of Mexico.
"Of course I don't want to cover up any of that. On the contrary, I exhort you to fight every day against corruption, against trafficking, against war, against division, against organized crime, against human smuggling."
Pena Nieto's government has drawn criticism for failing to go after corrupt politicians, even those indicted in the United States. He, his wife and his finance minister have all been embroiled in conflict-of-interest scandals over houses purchased from government contractors.
Father Federico Lombardi, the Vatican spokesman, said the Pope wants to visit parts of Mexico a pontiff had not visited before, and that the Mass in Ciudad Juarez "is a symbol of his concern for migrants".
Illegal immigration is a major issue in the U.S. presidential election campaign with Republican hopeful Donald Trump vowing to put up a wall along the border if he is elected and forcing Mexico to pay for it.
"The Mass is being intentionally held right on the border so that it will be visible from both sides," Lombardi said. "It´s a fence, it´s not a Chinese wall."
The Vatican expects a crowd of at least 200,000 on the Mexican side and of 50,000 on the U.S. side.
(Additional reporting by Philip Pullella in Vatican City and Anahi Rama in Mexico City; Writing by Simon Gardner; Editing by Kieran Murray)