(ANSA) - Vatican City, January 26 - Pope John Paul II used to whip himself regularly in an act of penance, according to the church official heading the Vatican's cause for the late pontiff's canonization, Slawomir Oder.

A new book by Oder, which appears in Italian bookshops on Wednesday, reveals that John Paul subjected himself to regular self-mortification as part of his devotional practices. ''Members of his closest entourage, both in Poland and the Vatican, heard with their own ears how Karol Wojtyla used to whip himself,'' writes Oder.

''There used to be a particular belt, intended for trousers, hanging from a hook in his wardrobe among all his robes.

''He used this as a whip and always brought it with him when he went to [the papal summer residence] Castel Gandolfo''. Oder's book confirms claims made late last year by a nun that cared for the pope, Sister Tobiana Sobodka, while giving evidence to the Vatican body considering John Paul's canonization. Sobodka, who was in the room next to the pontiff at his summer residence, told the body: ''We would hear the sound of the blows''.

According to Oder, self-flagellation was one of many ways in which the elderly pope sought to control his body. He not only fasted on prescribed days and throughout Lent, when he ate only one meal a day, he also abstained from food before carrying out any ordinations. He would frequently sleep on a cold, hard floor rather than in a bed, a practice he engaged in since at least the 1960s - although he would apparently rumple the blankets to make it appear he had slept in them, said Oder. While self-flagellation is no longer common in the Catholic Church, Vatican observers say the revelations about John Paul will provide the committee considering his canonization with further evidence of his religious commitment. The book, 'Perche' e' santo' (Why He Is A Saint), also reveals that the late pope had left instructions for his resignation in the event of an incurable illness. In two handwritten documents, made public for the first time in the new book, the ailing pope also spelled out his determination to continue his duties for as long as his health would permit. In the first document, dated 1989, he declared his intention to renounce his apostolic duties ''in the case of a lengthy illness, thought to be incurable that prevents me from carrying out my duties sufficiently''.

However, the document leaves the final decision in the hands of the Church cardinals, who chose not to take any action during the pontiff's final months of 2005.

In another letter, dated 1994, John Paul again said he felt it right to step down in the face of incurable disease but said unless this occurred, ''I feel it is a serious conscientious obligation to continue carrying out the task given to me [by God]''.

Another section of the book reveals that shortly before the 1981 assassination attempt on the pope's life, John Paul had learned that the Italian militant group the Red Brigades were planning to kidnap him. ''Shortly before the attack, the Italian secret services warned that the Red Brigade terrorists had a plan to kidnap John Paul,'' the book reported. According to Oder, this was why, when travelling to hospital in an ambulance after the attack, the pope remarked to his secretary, ''Just like Bachelet,'' in reference to the previous Red Brigades assassination of a Catholic judge Vittorio Bachelet.

Speaking at the presentation of his book, co-authored with journalist Saverio Gaeta, Oder said there was no certainty over when John Paul would be beatified.

He said the process was ''well under way'' but warned that the Congregation of the Saints, in charge of the canonization process, still needed to recognize a miracle by John Paul. ''There are still various stages to undergo and we don't yet know when the process will conclude,'' he said.

Last month, Benedict announced that John Paul had been proclaimed 'Venerable', the second in the four-stage process towards canonization.

Beatification is the final stage on the way to being declared a saint. It means someone can be called 'Blessed' and can be venerated by Catholics in the place where he or she lived. A saint is venerated by the entire Church.

During John Paul's funeral in 2005, crowds held up placards saying 'Santo Subito!', calling for the Polish pope to be declared a saint without going through the normal procedures.

Pope Benedict XVI has already accelerated procedures for his predecessor, waiving a rule that says the process cannot begin until at least five years have passed after the candidate's death.