Vatican City - Pope Francis has canceled his planned trip to attend the COP28 climate change conference in Dubai due to ongoing respiratory illness, a spokesperson for the Holy See said on Tuesday evening.

Despite the fact that the pope's state of health has been improving, his doctors had asked him to cancel the three-day journey, spokesperson Matteo Bruni said.

"Pope Francis has accepted the doctors' request with great regret and the trip has therefore been canceled," he added.

The 86-year-old head of the Roman Catholic Church has been suffering from a mild case of flu and inflammation in his lungs and respiratory tract since last weekend, according to the Vatican, which forced him to cancel several appointments.

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He also had to hold the traditional Angelus prayer from his residence and had large parts of his address read out by a priest. Francis appeared exhausted, was coughing and had to be treated intravenously with antibiotics.

The pontiff was due to attend a UN Climate Change Conference for the first time. He was scheduled to travel to Dubai from Friday to Sunday for the COP28 summit.

It was initially unclear whether Francis would instead be connected via video link for his planned speech.

There is now renewed concern about the pope's health among Catholics worldwide.

Francis, who will turn 87 in December, has been dealing with health issues for some time. He has already been treated in hospital twice this year, first because of pneumonia, followed by open abdominal surgery under general anesthetic.