As Pope Francis continued to show "some" improvement in his lab tests, the pontiff remained hospitalized with a respiratory tract infection on Sunday, the Vatican said.

Pope Francis, 88, read the newspapers and had breakfast on Sunday after a second night sleeping well at the hospital where he is being treated for a respiratory tract infection, the Vatican said.

Pope Francis, who has spent the last two nights in hospital, apologised for missing a mass at the Vatican on Sunday, saying that he was still being treated for bronchitis and thanking his doctors for looking after him.