(AFP) - Pope Francis said Wednesday that Benedict XVI, who in 2013 became the first pontiff to resign in six centuries, is "very ill" and urged people to pray for him.

The head of the worldwide Catholic Church later paid a visit to his 95-year-old predecessor at his home in a former convent inside the Vatican.

"Remember him, because he is very ill, asking the Lord to console and support him," Francis said.

A Vatican source told AFP that Benedict's health began deteriorating "about three days ago".

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

Vatican spokesman Matteo Bruni confirmed Benedict's health had worsened "in the last few hours" and said Francis had visited him after his audience.

"In the last few hours there has been a deterioration due to advancing age. The situation at the moment remains under control, monitored continually by doctors," Bruni said at 1030 GMT.

Benedict had cited his declining physical and mental health back in 2013 in his decision to become the first pope since 1415 to stand down as head of the worldwide Catholic church.

The pope emeritus, whose real name is Joseph Ratzinger, has since lived a quiet life, rarely appearing in public.

- 'Weak and fragile' -

Ratzinger was the first German pope for 1,000 years.

German Chancellor Olaf Scholz "wishes the pope emeritus a good recovery and sends his thoughts to him", said government spokeswoman Christiane Hoffmann.

Georg Baetzing, head of the German Bishops Conference, said his thoughts were with Benedict. His Italian counterpart, Matteo Zuppi, urged prayers for the ex-pontiff in Italy's churches.

The ANSA news agency reported that Benedict had complained of "respiratory problems" before Christmas, but he has long been in fragile health.

In 2018, in a letter sent to Italy's Corriere della Sera daily, Benedict described "the slow withering of my physical forces", saying he was "on an interior pilgrimage towards home".

Maltese Cardinal Mario Grech said in 2020 that Benedict "has difficulty in expressing himself".

The ex-pope, who uses a wheelchair, said "the Lord has taken away my speech in order to let me appreciate silence", Grech told Vatican News.

In April, Benedict's long-time secretary, Archbishop Georg Gaenswein, told Vatican News the ex-pope was "physically relatively weak and fragile", but "in good spirits".

- 'Deep remorse' -

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

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

Benedict's papacy was beset by Church infighting and the outcry over paedophilia.

He became the first pontiff to apologise for scandals over clerical sex abuse of children that emerged around the world, expressing "deep remorse" and meeting with victims in person.

But while he took key steps to tackle the issue, Benedict was criticised for failing to end Church cover-ups.

The paedophilia scandal has returned to haunt him in retirement.

A damning report for the German church in January 2022 accused him of personally having failed to stop four predatory priests in the 1980s while archbishop of Munich.

Benedict has denied wrongdoing and the Vatican has strongly defended his record.

- God's Rottweiler -

Unlike his successor Pope Francis, a Jesuit who delights in being among his flock, Benedict is considered a conservative intellectual.

He was dubbed "God's Rottweiler" in a previous post as chief doctrinal enforcer.

But as pontiff he appeared overwhelmed by the challenges facing a Church that was losing influence and followers, and the years of Vatican turmoil took their toll.

He stepped down in February 2013 in an announcement delivered to cardinals in Latin, later saying the decision was the result of a mystical experience.

Eleonora Matsechek, 19, who was in Saint Peter's Square on Wednesday, said his death would be "sad, because he was a good pope".

"He was brave to have resigned," she said.

In Bavaria, southern Germany, where Ratzinger once worked -- and where he brother Georg led the scandal-hit cathedral choir -- 62-year-old Erich Wagner expressed surprise at the news.

"I read in the newspaper just a couple of days ago that he's doing well... Nothing suggested that he was in such bad shape."

And Heike Marx-Teykal, 57, preferred not to judge him too harshly for the controversy surrounding his time as pope.

"He's just a human being and you shouldn't forget that," she said.

Francis, 86, has said he may also resign at some point.

He revealed for the first time in an interview this month that he had signed a resignation letter nearly a decade ago should poor health prevent him from carrying out his duties.

© Agence France-Presse