The health of Pope Emeritus Benedict XVI has worsened due to his age, and doctors are constantly monitoring the 95-year-old’s condition, the Vatican has said.

Vatican spokesperson Matteo Bruni said Pope Francis, who asked the faithful earlier on Wednesday to pray for Benedict, went to visit his predecessor in the monastery on Vatican grounds where the retired pontiff has lived since retiring in February 2013.

“Regarding the health conditions of the emeritus pope, for whom Pope Francis asked for prayers at the end of his general audience this morning, I can confirm that in the last hours, a worsening due to advanced age has happened,” Mr Bruni said in a written statement.

“The situation at the moment remains under control, constantly monitored by doctors,” according to the statement.

Pope Francis earlier said his predecessor is “very sick”, and he asked the faithful to pray for the retired pontiff so God will comfort him “to the very end”.

Pope Francis did not immediately elaborate on the condition of Benedict, who was the first pope to retire in 600 years, but the Vatican later confirmed his “worsening” health.

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Pope Francis delivers his blessing as he attends the weekly general audience in the Paul VI Hall at the Vatican on Wednesday (Alessandra Tarantino/AP/PA)

Benedict has become increasingly frail in recent years as he dedicated his post-papacy life to prayer and meditation.

“I would like to ask you all for a special prayer for Pope Emeritus Benedict, who is sustaining the church in silence,” Pope Francis said.

“Remember him — he is very ill — asking the Lord to console him and to sustain him in this testimony to love for the church, until the end.”

When Benedict turned 95 in April, his longtime secretary, Archbishop Georg Gaenswein, said the retired pontiff was in good spirits, adding that “naturally he is physically relatively weak and fragile, but rather lucid.”

In one of his previously publicised visits, Pope Francis had called on Benedict at the monastery four months ago. That occasion was Pope Francis’ latest ceremony elevating churchmen to cardinal rank, and the new “princes of the church” accompanied him to the monastery for the brief greeting.

The Vatican released a photo at the time that showed a very thin-looking Benedict clasping a hand of Francis as the current and past pontiff smiled at each other.

In his first years of retirement, Benedict attended a couple of cardinal-elevating ceremonies in St Peter’s Basilica. But in recent years, he wasn’t strong enough to attend the long service.

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Pope Francis, left, embraces emeritus pope Benedict at the Vatican in June 2017 (L’Osservatore Romano/Pool Photo via AP/PA)

He was elevated to cardinal’s rank in 1977 by the then-pontiff, Paul VI. As Cardinal Joseph Ratzinger, the German prelate and theologian long served as the Vatican’s doctrinal orthodox watchdog. He was elected pontiff in 2005.

In Benedict’s native Germany, the head of the nation’s bishops’ conference, Limburg Bishop Georg Baetzing, joined in Francis’s call for prayers.

“My thoughts are with the emeritus pope,” Bishop Baetzing told German news agency dpa. “I call on the faithful in Germany to pray for Benedict XVI.”

In Berlin, Chancellor Olaf Scholz “wishes the German pope, as we say, a good recovery and his thoughts are with him,” government spokesperson Christiane Hoffmann said during a regular government news conference.