The Vatican has excommunicated Archbishop Carlo Maria Vigano, one of Pope Francis's most virulent critics, after judging him guilty of splitting the Church, the dicastery in charge of doctrine said Friday.

The 83-year-old ultra conservative, who has called in the past for Francis to resign as pope, has been on trial since last month after being accused by the Dicastery for the Doctrine of the Faith of the crime of schism, or splitting the Catholic Church.

"His public statements manifesting his refusal to recognise and submit to the Supreme Pontiff, his rejection of communion with the members of the Church subject to him, and of the legitimacy and magisterial authority of the Second Vatican Council are well known," wrote the dicastery in a statement.

"At the conclusion of the penal process, the Most Reverend Carlo Maria Vigano was found guilty of the reserved delict of schism," it wrote, adding that his punishment was "excommunication" in accordance with canon law.

An excommunicated Catholic is prohibited from administering and receiving the sacraments and from exercising ecclesiastical functions, according to canon law.

Vigano -- who served as the Vatican's papal envoy to the United States from 2011 to 2016 and who is backed by an ultra-conservative US church faction -- has been an outspoken critic of Francis, going so far as accusing him of heresy.

In announcing last month that he had been summoned to appear before the powerful dicastery, which is charged with defending Catholic doctrine, the retired archbishop wrote on X: "I regard the accusations against me as an honour."

He did not appear before the tribunal, which judged him in absentia.

In a pages-long declaration, Vigano railed against Francis's welcome for undocumented migrants, his "delirious encyclicals" about climate change and authorisation of blessings for same-sex couples, and accused him of promoting his allies.

"I accuse Jorge Mario Bergoglio of heresy and schism, and I ask that he be judged as a heretic and schismatic and removed from the Throne which he has unworthily occupied for over eleven years," he wrote last month, using the Argentine pope's given name.

Vigano is allied with staunch traditionalists within the Church, especially in the United States, who have battled Francis's more progressive moves on liturgical or social issues, such as the Latin Mass or welcoming LGBTQ people into the Church.

Accusing him of sowing confusion and failing to uphold key Catholic beliefs, they have sometimes called into question the legitimacy of Francis as leader of the world's 1.3 million Catholics -- raising fears of a rupture within the Church.

In 2018, Vigano made headlines by calling for Francis's resignation, publishing a scathing list of accusations over the pope's management of sexual abuse cases within the Church.

In particular, Vigano accused Francis of having long protected former American cardinal Theodore McCarrick, who was defrocked a year later for sexual abuse against a minor.

Vigano again caused a major scandal in 2019 by publishing a long letter of unconditional support for then-US President Donald Trump, criticizing confinement measures during the Covid pandemic and defending a crackdown on rioters in the United States.

In November, in a rare move, Francis dismissed US bishop Joseph Strickland, a prominent conservative who had repeatedly criticised his papacy from his Tyler, Texas diocese.