He had announced that he would be admitted for the operation during his weekly Sunday prayers, telling the crowd in St Peter's Square that doctors had found a "well-contained" nodule on his lung "at an early stage" and advised him to have it removed.

Nodules are quite common and not necessarily cancerous, but after it was examined the medical team confirmed it was, "as suspected by pre-operative tests", the Vatican said. He was diagnosed with lung adenocarcinoma.

A Vatican source told news agency AFP that further tests were carried out to see whether the cancer had spread.

The Vatican has stressed that the Pope, who is generally thought to be fit, had no symptoms of infection or illness.

The news has shaken Catholics worldwide, many of whom will have recent memories of Pope Francis's hospital visits.

Pope Leo's predecessor, who died last year, also had part of his lung removed in his youth before suffering a series of respiratory infections later in life.

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