Pope Benedict XVI addresses cardinals in the Clementine Hall at the Vatican in 2009. The Vatican slammed a "sexual morality" book written by an American Catholic nun, warning believers to stay away from the tome which justifies masturbation, homosexuality and divorce

The Vatican slammed a "sexual morality" book written by an American Catholic nun on Monday, warning believers to stay away from the tome which justifies masturbation, homosexuality and divorce.

Margaret Farley's 2006 book "Just Love - A Framework for Christian Sexual Ethics" "affirms positions that are in direct contradiction with Catholic teaching in the field of sexual morality," the Vatican said in a statement.

Farley, a member of the Sisters of Mercy and professor emerita at Yale Divinity School, expressed support for a long list of sins in the eyes of the Church.

"Masturbation usually does not raise any moral questions at all. It is surely the case that many women have found great good in self-pleasuring... (which) actually serves relationships rather than hindering them," she wrote.

On the issue of homosexuality, the prominent theologian said "same-sex relationships and activities can be justified according to the same sexual ethic as heterosexual relationships and activities" and "should be respected."

She also said not all marriages could last and supported both divorce for people who are irrevocably unhappy together and remarriage with new partners.

The Congregation for the Doctrine of the Faith (CDF), which had been carrying out an investigation into the book, responded with a scathing criticism which tackled each of the issues Farley had raised.

It insisted that "masturbation is an intrinsically and gravely disordered action", homosexual relations are "acts of grave depravity", and "a marriage cannot be dissolved by any human power or for any reason other than death."

"The Congregation warns the faithful that the book is not in conformity with the teaching of the Church. Consequently it cannot be used as a valid expression of Catholic teaching," it said.

Last week the Leadership Conference of Women Religious (LCWR), the main US association of Catholic nuns, defended itself against CDF accusations of "corporate dissent" over the Church's teachings, particularly concerning homosexuality.