Mother Teresa struggled with her faith in God for almost 50 years

Mother Teresa, who may be canonized as a saint by the Vatican later this year, had a deep crisis of faith in God for most part of her life, a set of her letters has revealed.

The correspondence, between Teresa and her confessors and superiors over a period of years, showed that she felt alone and in a state of spiritual pain from around 1949, roughly the time when she started taking care of the poor and dying in Kolkata.

The "Saint of the Gutter" died on September 5, 1997, nine days after her 87th birthday.

Although she publicly proclaimed that her heart belonged "entirely to the Heart of Jesus", she wrote to the Rev Michael Van Der Peet, a spiritual confidant, in September 1979, that "Jesus has a very special love for you. As for me, the silence and emptiness is so great that I look and do not see, listen and do not hear. The tongue moves (in prayer) but does not speak."

The letter was written just a few weeks before she received the Nobel Peace Prize for her charitable work. More than 40 other letters, many of which she had asked to be destroyed in her will, show her fighting off feelings of "darkness" and "torture" for the last nearly half-century of her life.

The letters are published for the first time in a new book titled Mother Teresa: Come Be My Light, edited by the Rev Brian Kolodiejchuk, a close friend.

He wrote that during that period, Mother Teresa did not feel God "in her heart or in the Eucharist".