Philip Pullella, Reuters

A document for a meeting of Catholic bishops from the Amazon, expected to evaluate ordaining elderly married men as priests for the vast region, says the Church should make "daring proposals."

Father Benigno Palilla, an exorcist for the diocese of Palermo, told Vatican Radio in February that he had performed about 50 exorcisms in the past two and a half years.

Since his election in 2013, Francis has several times called for an worldwide ban on capital punishment, prompting criticism from Church conservatives, particularly in the United States.

In his letter, former Pope Benedict disputed suggestions by conservatives that Francis' academic qualities were lacking, praising his successor as a "man of deep philosophical and theological formation" and praising an "interior continuity between the two pontificates".

Pope Francis on Sunday said Syria was being "martyred" by continued attacks killing civilians in the eastern Ghouta district, calling for an immediate end to violence and access to humanitarian aid.

"Afterwards we will still be like a bird in a cage but the cage will be bigger," he said. It is not easy. Suffering will continue. We will have to fight for every centimeter to increase the size of the cage," he said.

Pope Francis on Wednesday condemned the "evil" of fake news, saying journalists and social media users should shun and unmask manipulative "snake tactics" that foment division to serve political and economic interests.

"The native Amazonian peoples have probably never been so threatened on their own lands as they are at present," the pope told a crowd of indigenous people from more than 20 groups including the Harakbut, Esse-ejas, Shipibos, Ashaninkas, and Juni Kuin.

"Nuclear weapons must be banned," Francis said, quoting a document issued by Pope John XXIII at the height of the Cold War and adding that there is "no denying that the conflagration could be started by some chance and unforeseen circumstance".