Pope Francis remained in critical condition Monday but showed slight improvement in laboratory tests and resumed some work, the Vatican said, including calling a parish in Gaza City that he has kept in touch with since the war there began.

The Vatican described his condition as critical for the first time on Saturday, reporting that the 88-year-old Francis needed supplemental oxygen and blood transfusions after a "prolonged asthma-like respiratory crisis.

Francis was also given blood transfusions, according to the Vatican, after blood tests revealed he was suffering from thrombocytopenia, meaning the platelet count in his blood was too low, a condition the doctors said is associated with anemia. Infections and medical treatment may lower platelet count.