Pope Francis has pleaded for social justice and environmental respect for the Amazon basin, but failed to recommend that priests in the area could marry, a controversial idea recently discussed at a landmark episcopal meeting.

In a highly anticipated text, released on Wednesday, Francis exhorted his followers to "feel outrage" over the exploitation of indigenous people and the destruction of land devastated by illegal mining and deforestation.

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Notably absent in his text, however, was mention of priestly marriage, suggested by Amazon bishops during a three-week synod on the region last October as a way to increase the number of priests who could perform Mass and other rites in the remote area.

Instead, the first Jesuit pope argued for women and missionaries to take larger, more important roles in the region and advocated for better training for priests to better interact with Amazonian cultures.

Francis has weighed in before on the hotly debated question of whether to allow "viri probati" - married "men of proven virtue" - to join the priesthood in remote locations, a suggestion that has aroused fierce opposition from traditionalists within the Roman Catholic church.

In January 2019, Francis said he did not believe that optional celibacy should be allowed while conceding "some possibilities for far flung places", a statement that opened the door to speculation that he might make an exception for the Amazon.

Francis's papacy has been marked by a passionate defence of the world's marginalised people, whether the poor, migrants or prisoners, and his Amazon text focused on a "history of suffering" by the region's local populations.

Saying the Amazon's ecological problems should not be separated from social ones, he pleaded for justice for marginalised indigenous people forced out of their homes due to illegal deforestation and mining, to the outskirts of cities marked by "an increase of xenophobia, sexual exploitation and human trafficking".

"We need to feel outrage, as Moses did, as Jesus did, as God does in the face of injustice. It is not good for us to become inured to evil ... " wrote the pope, lashing out against businesses harming the land and its people.

"The businesses, national or international, which harm the Amazon and fail to respect the right of the original peoples to the land and its boundaries, and to self-determination and prior consent, should be called for what they are: injustice and crime," he wrote.

While apologising for "crimes committed against the native peoples during the so-called conquest of America", Francis acknowledged the challenges faced by the Church in remote areas of the Amazon today and urged bishops to encourage young missionaries to preach there.

"Efforts need to be made to configure ministry in such a way that it is at the service of a more frequent celebration of the Eucharist, even in the remotest and most isolated communities," the pope wrote, adding there was also a need for ministers who "can understand Amazonian sensibilities and cultures from within".

Nuns and even laywomen and men could assume more important responsibilities in the region, he said.

"It is not simply a question of facilitating a greater presence of ordained ministers who can celebrate the Eucharist," wrote Francis, in the closest reference to the idea of allowing priestly marriage in the region.

"Priests are necessary, but this does not mean that permanent deacons (of whom there should be many more in the Amazon region), religious women and laypersons cannot regularly assume important responsibilities for the growth of communities, and perform those functions ever more effectively with the aid of a suitable accompaniment."