The Mormon church has admitted that its founder was a polygamist who married a 14-year-old girl, breaking a lengthy silence about its history.

Joseph Smith, who wrote the Book of Mormon and established the Church of Jesus Christ of Latter-day Saints, is thought to have married as many as 50 women, but for years the senior church officials did not address the subject.

But this week the organization acknowledged that the practice took place, and named Helen Mar Kimball, 'who was sealed to Joseph several months before her 15th birthday.'

Polygamous: The Mormon church has admitted that its founder Joseph Smith (right) had many wives - including 14-year-old Helen Kimball (pictured left much later in life)

Public admission: The Church of Jesus Christ of the Latter-day Saints had stayed silent on the issue of Joseph Smith;s polygamy for years. Pictured is a statue of Smith and his first wife, Emma, in front of the church's Salt Lake City headquarters

Estimates have placed the total number of Smith's wives between 27 and 50, though the church said it is impossible to say for sure.

However, it suggested many of his marriages may not have involved sex, and that Smith was reluctant to adopt the practice, which was eventually banned in 1890.

An essay published by the church, based in Salt Lake City, Utah, describes how Smith said he was visited three times by angels between 1834 and 1842 who commanded him to marry more women, despite him already having a wife, Emma.

The third time, the essay says: 'The angel came with a drawn sword, threatening Joseph with destruction unless he went forward and obeyed the commandment fully.'

It is part of a recent push by the Church of Jesus Christ of Latter-day Saints to open up about sensitive issues within the faith, many of which are uncomfortable to discuss.

Other writings posted in the past couple of years have addressed sacred undergarments worn by devout members; a past ban on black men in the lay clergy; and the misconception that Mormons are taught they'll get their own planet in the afterlife.

Ban: Polygamy was outlawed by the Mormon church in 1890. Pictured are church leaders around that time, including Wilford Woodruff, the leader who ended the practice

The latest article also makes efforts to imply that the polygamous marriages may not have been sexual. It makes a distinction between some unions 'for time and eternity' - which can include sex - and some 'for eternity only', which are thought to have been celibate.

The new article about Smith's wives during the 1830s and 1840s in Kirtland, Ohio, and Nauvoo, Illinois, comes about 10 months after the church acknowledged polygamy was widely practiced among its members in the late 19th century.

'As a collection, these are remarkably revealing articles, continuing the new open and transparent philosophy of historical writing,' said Armand Mauss, a retired professor of sociology and religious studies at Washington State University.

The information will be surprising to many Latter-day Saints who either didn't know or were encouraged to dismiss speculation as anti-Mormon propaganda, Mauss said.

Splinter groups who call themselves fundamentalist Mormons still practice plural marriage, including Warren Jeffs' sect on the Utah-Arizona border.

Latter-day Saints began practicing polygamy after Smith received a revelation from God. He took his first plural wife in 1830 in Ohio, three years after he married his first wife, Emma, the article shows.

He and his first plural wife separated, but he renewed the practice a decade later in Illinois, which is where he married the teenager.

'Difficult': An essay published by the church describes Smith's reluctance to engage in plural marriage - and says the process was 'excruciating' for his first wife, Emma, depicted above

The essay noted that while inappropriate by today's standards, marriage among teen girls was legal at the time.

The article acknowledges that many details about polygamy in early Mormonism are hazy because members were taught to keep their actions confidential. But research has indicated that Smith's marriage to the young girl might not have involved sex.

Some plural marriages were designed to seal the man to the woman for eternity only, and not life and eternity as Mormons believe, the article says. Those types of marriages didn't seem to involve sex.

Little is known about Smith's marriages to the already-married women, the article says. They also might have been the type of unions that didn't involve sex.

Plural marriage was an 'excruciating ordeal' for Emma Smith and confounding for some men, too, the article says. Some people left the faith, and others refused to take multiple wives while remaining Latter-day Saints.

When Latter-day Saints trekked cross-country to Utah in 1847, nearly 200 men and more than 500 women were in plural marriage, it says.

'Difficult as it was, the introduction of plural marriage in Nauvoo did indeed 'raise up seed' unto God,' the article says. 'A substantial number of today's members descend through faithful Latter-day Saints who practiced plural marriage.'