The crisis was a new setback in the Pope's fight to recover from a complicated respiratory infection, which has lasted more than two weeks. Pope Francis has chronic lung disease and had part of one lung removed as a young man.

The 88-year-old pontiff has been hospitalized since Feb. 14 after a bout of bronchitis worsened and turned into a complex pneumonia in both lungs.

Pope Francis experienced more respiratory problems and went on noninvasive ventilation on Monday, the Vatican said, as the head of the Roman Catholic Church battles double pneumonia in the hospital.