(AFP) - Pope Francis denounced the use of violence in the struggle for indigenous rights Wednesday, celebrating mass in a restive region of Chile hours after assailants firebombed churches and other targets.

The Argentine-born pontiff was shining the spotlight on the simmering conflict between the state and the Mapuche people, who centuries ago controlled vast areas of Chile but have since been marginalized.

"You cannot assert yourself by destroying others, because this only leads to more violence and division," the pope said, speaking before thousands of faithful at an airfield in Temuco, the capital of the southern Araucania region.

"Violence begets violence, destruction increases fragmentation and separation. Violence eventually makes a most just cause into a lie," the pope warned.

Unidentified assailants hurled incendiary devices at three Catholic churches and an evangelical Christian church in pre-dawn attacks Wednesday in the Araucania region.

Five other churches had previously been hit by arsonists in Chile's capital Santiago.

A forestry company helicopter also was torched during the night, and a policeman was shot and wounded by a group of hooded assailants, authorities said.

The aim was to "cause disorder or disturbance of the public order" during the pope's visit to Temuco, said Chilean police chief Bruno Villalobos.

- Simmering conflict -

At the pope's first stop in Santiago -- his first to Chile as the leader of the world's 1.2 billion Catholics -- he faced protests over the church's handling of clergy sexual abuse.

In Temuco, however, the papal spotlight turned to the Mapuche, who account for seven percent of Chile's population but hold only five percent of their ancestral lands.

Francis met after the mass with a group of indigenous people before returning to Santiago, where he met with youth groups at the Maipu shrine outside the city. He was later to visit Chile's Catholic university.

Most of the pontiff's third day in Chile will be spent in the northern coastal city of Iquique, where Francis is scheduled to hold an open-air mass overlooking the Pacific Ocean. He then heads to Peru on the second leg of his South American visit.

Thousands waited from the early hours of Wednesday at the Maquehue airfield to hear the pope, who dedicated the mass to the victims of human rights abuses during the 1973-1990 dictatorship of Augusto Pinochet.

Pope Francis said he chose to celebrate mass at the airfield because of its history as a detention center during the military regime.

"This celebration we offer for all who suffered and died and for those who each day carry on their backs the weight of so many injustices," he said.

"I think it was worth it because for a long time in this country we have needed to hear the message that Pope Francis is bringing," said Jessica Pinto, who drove for more than three hours to see the pope.

- Sexual abuse -

On Tuesday in Santiago, the pope met privately with a small group of people sexually abused by priests, after he publicly asked for forgiveness.

During the "strictly private" meeting at the Vatican embassy in the capital, the victims "spoke of their suffering to Pope Francis, who listened to them and prayed and cried with them," the Vatican said.

Earlier, the 81-year-old pontiff said: "I cannot begin to express the pain and shame that I feel over the irreparable harm caused to children by some ministers of the church," vowing to commit to ensure the abuses would never happen again.

Francis made the comments during a visit to President Michelle Bachelet's official Moneda Palace residence, drawing applause from pilgrims watching on giant screens in a park where he later celebrated an open-air mass for some 400,000 people.

- 'Pedophile accomplices' -

But the pope did not receive a universal welcome.

Scuffles broke out between riot police and demonstrators near O'Higgins Park, and police deployed armored water cannons to hose demonstrators. More than 50 people were arrested, authorities said.

The pope's visit was preceded by the release of a report outlining the depth of sexual abuse in the local church, and his appointment of a bishop who many Chileans accuse of covering up the country's most prominent sex abuse scandal.

The US-based NGO Bishop Accountability said that almost 80 Roman Catholic clergy members had been accused of sexually abusing children in Chile since 2000.

A lingering controversy is the continued presence of 61-year-old Bishop Juan Barros at both of the pope's open-air masses and his meeting with clergy at the Santiago cathedral.

Local Catholic groups in his southern diocese of Osorno are demanding that Francis remove Barros for his ties to a disgraced pedophile priest, Fernando Karadima.

Barros "is a liar, a delinquent, who has amnesia after covering up for Karadima. He has covered-up abuses and should be in jail or at least dismissed," said Juan Carlos Cruz, one of Karadima's victims.

© Agence France-Presse