Pope Benedict XVI surprised the world on Monday by saying he no longer had the mental and physical strength to cope with the demands of his ministry, becoming the first pontiff to step down since the Middle Ages and leaving his aides "incredulous".

A Vatican spokesman said the Pope had not resigned because of "difficulties in the papacy" and the decision had been a surprise, indicating that even his closest aides were unaware that he was about to quit. The Pope does not fear schism in the Church after his resignation, the spokesman said.

In a statement, the pope said in order to govern "...both strength of mind and body are necessary, strength which in the last few months, has deteriorated in me to the extent that I have had to recognize my incapacity to adequately fulfill the ministry entrusted to me.

"For this reason, and well aware of the seriousness of this act, with full freedom I declare that I renounce the ministry of Bishop of Rome, Successor of Saint Peter."

A Vatican spokesman said the pontiff would step down from 2 p.m. ET on February 28, leaving the office vacant until a successor was chosen to Benedict who succeeded John Paul, one of history's most popular pontiffs.

He was elected to the papacy on April 19, 2005 succeeding the late Pope John Paul II. 

Two Africans, Nigeria Cardinal Francis Arinze and Ghanian Cardinal Peter Turkson, are said the strongest candidates to succeed Pope Benedict.

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