Pope Francis, 86, was admitted to a hospital in Rome on Wednesday, March 29 with a respiratory infection that will require a stay of a few days, the Vatican said.
"In recent days Pope Francis has complained of some breathing difficulties," Vatican spokesman Matteo Bruni said in a statement.
The pontiff was admitted to Rome's Gemelli hospital for medical checks, which revealed "a respiratory infection... that will require a few days of appropriate hospital medical treatment," Bruni said.
COVID-19 had been excluded, he added.
A Vatican source confirmed the pope's engagements on Thursday, March 30 were canceled, with others likely to follow in what is a very busy period for the pontiff ahead of the key Christian holiday of Easter.
Joe Biden, only the second Catholic president in US history, urged attendees at a Greek independence day reception at the White House on Wednesday to "say an extra prayer" for the pope.
Francis, who marked a decade as head of the Catholic Church earlier this month, spent 10 days in the Gemelli hospital in July 2021 after undergoing colon surgery.
He has also suffered pain in his knee, which has forced him to use a wheelchair, although he continues to travel widely.
"Pope Francis is touched by the many messages received and expresses his gratitude for the closeness and prayer," Bruni added in his statement.
At his weekly audience at the Vatican earlier Wednesday, the pope appeared in good spirits, smiling as he greeted the faithful in his popemobile.
However, he was seen grimacing as he was helped into the vehicle.
Dozens of journalists gathered late Wednesday outside the hospital, where a statue of the late pope John Paul II stands by the entrance.
The Vatican had first announced mid-afternoon that the pope had been admitted for what it described as "previously scheduled checks."
The pontiff underwent surgery in 2021 after suffering from a type of diverticulitis, an inflammation of pockets that develop in the lining of the intestine.
A year later he admitted he was still feeling the effects of six hours spent under anesthetic during the surgery.
In an interview in January, Francis said the diverticulitis had returned.
In a message Wednesday, the Italian Bishops' Conference offered their prayers for the pope's "rapid recovery."
Pope Francis had to cancel or curtail activities several times last year because of the pain in his knee and in a July 2022 interview acknowledged that he needed to slow down.
His health has been the frequent subject of speculation, particularly the question of whether he will follow the example set by his predecessor and retire if he cannot continue.
Benedict XVI, an eminent German theologian, shocked the world in 2013 by becoming the first pope since the Middle Ages to resign.
The two "men in white" co-existed within the walls of the tiny Vatican state for almost a decade, before Benedict died on Dec. 31.
Francis has said he would follow Benedict in stepping down if his health made him unable to do his job.
However, he told an interviewer in February that papal resignations should not become "a normal thing," adding that for the moment it was not on his agenda.
Despite his advancing age and health problems, Francis continues to travel.
Huge crowds greeted him on a visit earlier this year to South Sudan and the Democratic Republic of Congo, a testament to his ongoing popularity.
Next month, he is due to visit Hungary and meet Prime Minister Viktor Orban.
In the past decade, he has sought to forge an image of a more open, compassionate Church, although has faced internal opposition, particularly from conservatives.
Francis almost died when he was 21 after developing pleurisy and having part of his lungs removed.
He has since insisted he made "a complete recovery... and never felt any limitation since then." (AFP)