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The Church of Jesus Christ of Latter-day Saints has instructed local church leaders that same-sex couples are apostates and that children living with them can't take part in church activities until they're adults and leave home, the church told NBC News on Thursday night.

The policies are included in revisions of the Church Handbook of Instructions that were implemented Thursday and sent to leaders of local Mormon congregations, or stakes.

The revisions were approved by the church's Council of the First Presidency and its Quorum of the Twelve Apostles to clarify how stake leaders should proceed after decisions in the last year legalizing same-sex marriages by the U.S. Supreme Court and high courts in other countries.

Church critics blasted the hard-line approach.

"It is astounding and deeply disturbing for me to see the LDS church list legal same-sex marriage ... as a sin comparable to murder, rape, sexual abuse, spouse abuse," said John Dehlin, a gay-rights advocate and podcaster who was excommunicated earlier this year.

"What's even more disturbing about this new policy change is that the children of LDS murderers and rapists can still get baptized, but children of legally same-sex married couples cannot. This is troubling even by Mormon standards."

Members of the Church of Jesus Christ of Latter-day Saints attend the 185th Semiannual General Conference of the Mormon Church last month in Salt Lake City, Utah. George Frey / Getty Images

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Eric Hawkins, a spokesman for the church, which is based in Salt Lake City, Utah, told NBC News that the revisions had been in the works for some time and that their issuance Thursday was unrelated to the election of Jackie Biskupski as the city's first openly gay mayor this week.

"The church has long been on record as opposing same-sex marriages," Hawkins said. "While it respects the law of the land and acknowledges the right of others to think and act differently, it does not perform or accept same-sex marriage within its membership."

The revisions add those who are "in a same-gender marriage" to the list of apostates — that is, those who are considered to have turned their backs on their churches.

A separate section of the handbook includes new language instructing local leaders that a child — biological or adopted — of parents living in a same-gender relationship may not receive the church's blessing, begin training to become missionaries, or be baptized, confirmed or ordained without permission of top church leaders.

Even then, such approval would be allowed only if the child is 18 or older, leaves home and "specifically disavows the practice of same-gender cohabitation and marriage," according to the revisions.

The Mormon church typically baptizes children at age 8, and it has said that children so young aren't old enough to understand that their parents' relationship is contrary to the church's interpretation of God's laws.

Likewise, the official blessing of a child of Mormon parents starts a process that creates a church record tracking the child's education and spiritual guidance. The church says a young child isn't qualified to make informed choices in such a serious matter, according to the church.

Mormons were instrumental in the passage of California's Proposition 8, which made same-sex marriage illegal and was later found unconstitutional.

Early this year, the church endorsed bills that would bar discrimination against gay Americans in housing and employment, but at the same time, it also called for new laws to protect "religious freedoms."

In a letter to local LDS officers three days after the Supreme Court's June 26 ruling legalizing gay marriage, the church reiterated that "marriage between a man and a woman was instituted by God and is central to His plan for His children and for the well-being of society."

It's a position church officials have informally dubbed "fairness for all."

But Equality Utah, an advocacy group for lesbian, gay and transgender people, said Thursday's announcements were "directly aimed" at destroying same-sex couples.

"We support all families and believe that these divisive policies do not represent the Utah values of inclusion and respect," it said.