Pope Benedict XVI is to resign at the end of this month in an unexpected development, saying he is too old to continue at the age of 85.
He became Pope in 2005 following John Paul II’s death.
Resignations from the papacy are not unknown, but this is the first in the modern era, which has been marked by pontiffs dying while in office.
Italian Prime Minister Mario Monti is quoted as saying he is “greatly shaken by this unexpected news”.
The BBC’s Alan Johnston in Rome says the news has come “out of the blue”, and that there was no speculation whatsoever about the move in recent days.
A Vatican spokesman, Father Federico Lombardi, said that even the Pope’s closest aides did not know what he was planning to do and were left “incredulous”.
But the brother of the German-born Pope said the pontiff had been advised by his doctor not to take any more transatlantic trips and had been considering stepping down for months.
Talking from his home in Regensburg in Germany, Georg Ratzinger said his brother was having increasing difficulty walking and that his resignation was part of a “natural process”.
He added: “His age is weighing on him. At this age my brother wants more rest.”
‘Incapacity’
At 78, the former Cardinal Joseph Ratzinger was one of the oldest new popes in history when elected.
He took the helm as one of the fiercest storms the Catholic Church has faced in decades – the scandal of child sex abuse by priests – was breaking.