Berliner Tageblatt - Ex-pope Benedict's health serious but stable: media

"His situation has not changed from yesterday," an unnamed source in contact with those around the German ex-pontiff told ANSA news agency, adding that doctors were continually monitoring his health.

Contacted by AFP, the Vatican neither confirmed or denied the report.

Benedict, who in 2013 became the first pope since the Middle Ages to resign as head of the worldwide Catholic Church, has been in fragile health for many years.

But Pope Francis sparked alarm on Wednesday by revealing at his general audience that his predecessor, whose birth name is Joseph Ratzinger, was "very ill".

He called for people to pray for him, before going to visit Benedict at the monastery in the Vatican grounds where he lives.

The Vatican later confirmed his health had worsened, while a Vatican source told AFP on Wednesday that it began deteriorating "about three days ago".

"It is his vital functions that are failing, including his heart," the source said, adding that no hospitalisation was planned, as he has the "necessary medical equipment" at home.

Benedict had cited his declining physical and mental health in his decision to stand down.

His resignation created an unprecedented situation in which two "men in white" -- Benedict and Pope Francis -- have co-existed within the walls of the tiny city state.

Benedict was 78 when he succeeded the long-reigning and popular John Paul II in April 2005.

He was known for being a brilliant theologian, but his papacy was beset by Church infighting and the outcry over clerical sex abuse of children.

He became the first pontiff to apologise for the abuse that emerged around the world, expressing "deep remorse" and meeting with victims in person, but critics said he did not do enough.

In 2012, his butler Paolo Gabriele leaked secret papers to the media, an act seen as betrayal which profoundly affected the pontiff.

His papacy was also marred by a money-laundering scandal at the Vatican bank, which exposed infighting among Benedict's closest allies.

I.Meyer--BTB