Vatican City - Pope Francis has approved the canonization of two new saints from his hospital bed, the Vatican said Tuesday, as the 88-year-old pontiff, who has pneumonia in both lungs, remained hospitalized for a 12th day.

Despite his critical condition, the leader of the world's nearly 1.4 billion Catholics has striven to keep up with Church matters during his stay, according to the Vatican.

After revealing a "slight improvement" in the Argentine pope's condition Monday evening, the Vatican said Tuesday that he had received its secretary of state, Cardinal Pietro Parolin, the day before, and his number two, Venezuelan Archbishop Edgar Pena Parra.

Francis approved the canonization of two Venezuelan and Italian laymen who died in the early 20th century while authorizing the first steps towards sainthood for three 19th-century priests from Spain, Italy, and Poland, the Vatican said.

World Pope Francis shares personal message as hospital stay continues

The pope has been working from his special papal suite on the 10th floor of Rome's Gemelli hospital, where he was admitted on February 14 with breathing difficulties.

His condition worsened, with asthmatic respiratory attacks over the weekend that required high levels of oxygen and blood transfusions to combat anemia.

Catholics across the globe have gathered to pray for the pope as some expressed hope he may have turned a corner on what doctors warn could be a long path to recovery.

The Vatican's Monday update offered a glimmer of light, saying that Francis had suffered no new respiratory attacks that required "high-flow oxygen" and that his laboratory tests had improved.

He had also called the Gaza parish priest, as he has routinely done since the war broke out, the Vatican said. This time, he was thanking him for a video the parish sent him.

"The whole world is praying for you... and everyone wishes you good health", the priest said in the video, which was published on Vatican News and showed him surrounded by his flock.

The pope remains fragile, and his medical team has cautioned it will take time for drug treatments to show positive effects.

"Considering the complexity of the clinical picture," his doctors decline to "decide on the prognosis", the Vatican said Monday.