VATICAN CITY (Reuters) - Pope Francis canonized 35 new Roman Catholic saints on Sunday, including three indigenous children martyred in 16th century Mexico and considered the first Christians killed for their faith in the New World.

Francis used the occasion to announce that he had decided to call a meeting of bishops, or synod, from countries in the Pan-Amazon region for October, 2019, to discuss the condition of the Church in the area and the plight of indigenous people.

The region includes Guyana, Suriname, French Guyana, Venezuela, Ecuador, Colombia, Bolivia, Peru and Brazil.

The three children the pope canonized before a crowd of tens of thousands in St. Peter’s Square were of the Talaxcaltec people, an indigenous pre-Colombian group in what is now Mexico.

The first child, Cristoforo, was converted to Christianity by Franciscan missionaries and was killed in 1527 by his own father, a tribal chief who spurned his son’s attempts to convert him from paganism.

The boy was beaten and thrown into a fire when he was 13.

Two other indigenous children from the same area, Antonio and Juan, were killed by Indios in the village of Cuauhtinchan in 1529 as a result of their conversion. They are believed to have been 12 or 13 when they were beaten to death for helping Dominican missionaries.

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The pope also canonized 30 martyrs who were killed for their faith in Brazil in 1645. They included two Portuguese missionaries and 28 followers killed by Dutch colonial soldiers during a period of persecution of Catholics.

In announcing the 2019 synod for bishops from the Amazon region, Francis said indigenous people there today were “often abandoned and without the prospect of a bright future, even due to the crisis of the Amazon Forest, a lung of utmost importance for our planet”.

Francis, an Argentine and the first Latin American pope, has often linked his calls for social justice, particularly for indigenous people, to those for defense of the environment, saying the poor will suffer the most from the effects of climate change.

In 2015 he wrote a landmark encyclical, or papal letter, on defense of the environment and he has called for special protection for the Amazon region because of its vital importance to the planet’s ecosystem.

In his comments on Sunday, the pope did not mention the role of the Church in suppressing native cultures in the New World.

But during a visit to Bolivia in 2015, Francis said “many grave sins were committed against the native people of America in the name of God”. He asked forgiveness for the Church, for “crimes committed against native peoples during the so-called conquest of America”.

On Sunday, Francis also canonized Father Faustino Miguez, a Spanish priest who lived in the 19th and 20th centuries, and Father Angelo d’Acri, an Italian itinerant preacher who died in 1739 after serving in some of the most remote areas of mountainous southern Italy.