India, Feb. 24 -- Pope Francis, who is currently undergoing treatment for double pneumonia, is now facing a new challenge in his ongoing health struggle - "initial, slight insufficiency" in his kidney function, the Vatican said on Sunday.

"The condition of the Holy Father remains critical; however, since last night he has not experienced further respiratory crises," the Vatican statement said.

Blood tests also indicated "an initial, slight renal insufficiency, which is currently under control," it said, referring to the functioning of the kidneys, which filter waste products in the blood.

The Vatican also confirmed that the 88-year-old pontiff remains in critical condition, a day after he required a blood transfusion due to a "prolonge...