Pope Francis on Sunday expressed confidence in his treatment in a message published in place of his weekly Angelus prayer, as the 88-year-old remained in hospital for a tenth consecutive day.

Vatican sources said the text was written in the past few days- likely before the pontiff suffered a respiratory attack on Saturday, after which the Holy See warned his condition "continues to be critical".

"I am confidently continuing my hospitalisation at the Gemelli Hospital, carrying on with the necessary treatment- and rest is also part of the therapy!" the pontiff wrote in the statement. He thanked the doctors and health workers at the hospital, where he was admitted on February 14 with bronchitis, which developed into double pneumonia.

Vatican sources said Sunday he was still receiving oxygen through a tube tucked into his nose. "In recent days, I have received many messages of affection, and I have been particularly struck by the letters and drawings from children," the pope added.

"Thank you for this closeness and for the prayers of comfort I have received from all over the world! I entrust you all to the intercession of Mary, and I ask you to pray for me."

The pope normally delivers his Angelus prayer from the window of the Apostolic Palace at the Vatican, finishing by asking the crowds gathered in St Peter's Square below to pray for him and have a good lunch.

He usually calls for peace and did so again on Sunday, marking the third anniversary of Russia's invasion of Ukraine on Monday. "Tomorrow will be the third anniversary of the large-scale war against Ukraine, a painful and shameful occasion for the whole of humanity!" he wrote.

"As I reiterate my closeness to the suffering Ukrainian people, I invite you to remember the victims of all armed conflicts and to pray for the gift of peace in Palestine, Israel and throughout the Middle East, Myanmar, Kivu and Sudan."