Child sex abuse allegations have prompted pointed accusations of a coverup within the Catholic Church but also intense scrutiny over the actions of Pope Francis, with a former Vatican ambassador to Washington calling for his resignation.

Francis has given no indication he has any plans to step down, and the decision to leave the papacy could be made only through his own volition, as there are effectively no other measures in which a pope can be ousted, say some theologians.

"There are only two circumstances that can lead to him no longer being pope, and one would be his death and then the other would be his free resignation," said Monsignor Jason Gray, a canon lawyer and pastor based in Illinois.

The Catholic Church has recently come under fire following the release of a grand jury report that claimed hundreds of Roman Catholic priests in Pennsylvania committed sexual abuse against children since the 1940s.

Powers of the pontiff

In the wake of the grand jury report, Archbishop Carlo Maria Vigano, the former Vatican ambassador to Washington, called for the Pope's resignation. In an 11-page letter released to the Catholic media, Vigano accused Francis of having known of allegations of sex abuse by a prominent U.S. cardinal, Theodore McCarrick, for years and called on the Pope to set a good example and resign.

The Pope has said he will not respond to the allegations, and Vigano has provided no evidence to substantiate the accusation.

Ex-cardinal Theodore McCarrick, right, resigned in July after a review concluded that claims he had sexually abused a 16-year-old boy were credible. (Jonathan Newton/The Washington Post/Associated Press)

But the 1983 Code of Canon Law, sets out rules and obligations for the Catholic clergy and faithful, including the powers of the pontiff.

Canon 331, for example, states that by the virtue of his office, the pope "possesses supreme, full, immediate, and universal ordinary power in the Church, which he is always able to exercise freely."

This means, quite simply, that the pope is the supreme authority in the Catholic Church, said Gray.

'The First See is judged by no one'

Meanwhile, Canon 1404 states: "The First See is judged by no one." Based on that, "the short answer is that ther​e is no authority in the Church that can order or compel the Pope to resign," Gray said.

And that is true even if the pope were to become severely incapacitated, either through illness, or age, said Edward Peters, a professor of canon law at the Sacred Heart Major Seminary of the Archdiocese of Detroit.

"There is an old saying, "The Church knows how to deal with a live pope, and she knows how to deal with a dead pope. But a sick pope, that is real trouble,'" Peters said.

Massimo Faggioli, a professor of theology and religious studies at Villanova University in Pennsylvania, said that John Paul II was incapacitated in the last months of his life, and it was well known that his personal secretary was making decisions on his behalf.

'The institution can run out of luck'

But in general, popes have died in office before the papacy had to deal with "some very significant obstacles" in the pontiff's health or behaviour, Faggioli said.

Pope Benedict was aware of this risk when he decided to resign because of his declining health, Faggioli said.

"He knew the institution can run out of luck," he said.

If a pope does decide to resign, then, according to Canon 332, "it is required for validity that the resignation is made freely and properly manifested."

So, "if there is a reasonable doubt that the resignation of the pope has been made not in freedom by the pope then, in theory, according to the law of the Church, it is not valid," Faggioli said.

A coup d'etat in the making?

But a pope could conclude he must leave office for the good of the Church if media coverage and public perception of the pontiff becomes too negative, he said.

Some observers, including Faggioli, have stated that Vigano's letter was more about conservative opposition to Francis's liberalization of the Church than his concern about abuse coverups.

Faggioli suspects Vigano was attempting to engender public antipathy for the Pope that would effectively force him out.

Archbishop Carlo Maria Vigano, the former Vatican ambassador to Washington, called for the Pope's resignation, claiming he knew about McCarrick's crime. Some have called Vigano's move an attempted coup d'etat. (The Associated Press)

"That had all the characteristics of a coup d'etat. Not just asking the Pope to resign but also publishing that while the Pope is out of Rome, right in the middle of the summer."

The only way, it seems, that a pope could lose his authority, is if he is determined to have committed heresy. According to the Code of Canon law, heresy is defined as "the obstinate denial or obstinate doubt after the reception of baptism of some truth that must be believed by divine and Catholic faith."

"There is a sense that a person does lose their office by defecting from the faith," Gray said. "Now, the problem is when we talk about a mechanism, there's no mechanism to provide for that."

Since canon law doesn't specify who would determine whether the pope has committed heresy but does state that the pontiff is the highest authority, not to be judged by anyone, the question of how he would be removed is a bit of a grey zone, says Peters.

Still, in a 2016 post on his popular blog on canon law, Peters cited others who suggest a general council of bishops could make that determination and the pope would automatically lose power.

"However difficult it might be to determine whether a pope has so fallen, such a catastrophe ... would result in the loss of papal office," Peters wrote.

With files from Reuters