The Mormon church has issued its most comprehensive explanation yet about its past exclusion of black people from the priesthood.

The statement disavowing previous teachings was posted on the Church of Jesus Christ of Latter-day Saints' website.

It says an era of great racial divide influenced the early teachings of the church, founded in 1830. The article pins the ban on an announcement in 1852 from Brigham Young, the church's then president.

The church barred men of African descent from the lay clergy until 1978, when church leaders had a revelation. In the 35 years since that landmark moment, however, the church had never explained the reasons behind the ban or addressed the once widely held notion that black people were spiritually inferior, said Matthew Bowman, an author and assistant professor of religion at Hampden-Sydney College in Virginia.

In the new article, posted on Friday, the church finally addresses what had become a sensitive topic for current leaders and members.

"The church disavows the theories advanced in the past that black skin is a sign of divine disfavour or curse, or that it reflects actions in a premortal life; that mixed-race marriages are a sin; or that blacks or people of any other race or ethnicity are inferior in any way to anyone else," the statement read. "Church leaders today unequivocally condemn all racism, past and present, in any form."

Mormon church officials declined to comment on the article but said it was part of a series of new online postings to explain or expand on certain gospel topics for its members. Other topics include, "Are Mormons Christian?" and one about founder Joseph Smith's first visions.

The nearly 2,000-word article is the most comprehensive explanation yet about the past exclusion of black people from the priesthood and marks the first time the church has explicitly disavowed its previous teachings on the topic, said Armand Mauss, a retired professor of sociology and religious studies at Washington State University.

Mormon scholars over the years have written much of what is in the posting, but it is noteworthy that it comes from church headquarters in Salt Lake City, he said. Mauss and other scholars were interviewed several months ago by staff from Latter Day Saints' public affairs in preparation for the new article, he said, adding that it reflects a "new church commitment to greater transparency about its history, doctrines, and policies".

Don Harwell, an African American who converted to Mormonism in 1983, called it a great moment.

"History and changes all happen due to time. This is way past due," said Harwell, 67. "These are the statements they should have made in 1978, but better late than never."

Harwell is the president of Utah's Genesis Group, a support organisation for black Mormons. He pointed out that he does not speak for the church, but said he believes the next step is getting more black Mormons into church leadership positions.

Margaret Blair Young, an adjunct professor at Brigham Young University who made a documentary about the untold stories of black Mormons, called the new article a miracle.

"I'm thrilled," Young said. "It went so much further than anything before has done."