Pope Francis's condition is not currently critical, a Vatican source said Friday, after a series of clinical improvements for the 88-year-old pontiff suffering from pneumonia in both lungs. 

The Argentine pope has spent the past two weeks at Rome's Gemelli hospital, with the Vatican reporting incremental improvements in his condition in recent days. 

A Vatican source said Friday that the "criticality has passed, for the moment", while cautioning that Francis's overall condition "remains complex" and his prognosis still "reserved."

Earlier Friday, the Vatican said the Pope had spent another peaceful night in hospital. 

After being hospitalised on 14 February for breathing difficulties, the pontiff's condition sparked widespread alarm as it deteriorated into pneumonia in both lungs. 

But there has been no recurrence of the breathing attack he suffered at the weekend and since then the Vatican has released more optimistic medical updates.

On Monday, it said Francis showed a "slight improvement," and on Tuesday noted that his condition was "critical but stable," the last time it used the term "critical" for his condition. 

A "further, slight improvement" was reported Wednesday and on Thursday the Vatican said the "clinical conditions of the Holy Father are confirmed to be improving today also."

Still reserved

The Vatican has not yet modified the pope's prognosis of "reserved," however — which means doctors will not predict changes in his health.

Medical experts have warned that Francis's age and the chronic respiratory disease from which he suffers mean a sustained recovery could take time. 

"Given the complexity of the clinical picture, further days of clinical stability are necessary to resolve the prognosis," the Vatican said Thursday.

Francis — who has been pope since 2013 — has continued to work in hospital, where he is in a special papal suite on the 10th floor.

He also has been doing breathing exercises in between resting and praying, according to the Vatican. 

This hospital stay is the fourth of his nearly 12-year papacy, and his longest. 

In recent years, he has had surgery on his colon, a hernia operation and pain in his knee and hip that have caused him to rely on a wheelchair. 

There has been speculation as to whether Francis might now resign, especially as his schedule has been packed with papal duties amid celebrations for the holy Jubilee year.

"If the Pope survives, many imagine that he will want to finish the Jubilee year, but that afterwards, when he is 89, he will face the question of whether or not to resign," Italian Vatican expert Marco Politi told AFP.

Francis has always been open to following his predecessor, Benedict XVI, who in 2013 stepped down because of his physical and mental health. 

But the Argentine Pope, before his hospitalisation, had repeatedly said it is not yet the time — and may never be.