Things are definitely heating up in the US Republican presidential race, with Donald Trump saying he "doesn't know" about Ben Carson's Seventh-day Adventist Church in a veiled attempt to raise doubts on his top rival's faith. "I mean, Seventh-day Adventist, I don't know about," said Trump in a recent interview.

Coming to his own defence, the former neurosurgeon said his relationship with God is "the most important aspect" of his life but "it's not really denomination specific."

Carson then shared with The Associated Press how as a Yale college student, he doubted whether he should stay or not in the Seventh-day Adventist Church. He was very upset because of the segregation in his church, so he tried out services at Roman Catholic, Methodist, Baptist and Lutheran churches. Nothing really stuck with him, so he ended up staying with the Seventh-day Adventist Church.

"I concluded it was the right church, just the wrong people. The church was very segregated. You know, if you have the love of God in your heart, it seems like you wouldn't do that. That has changed fairly significantly since that time," Carson said.

He admitted that it was also a "huge mistake" for the Adventist policy-making body to vote against ordaining women. "I don't see any reason why women can't be ordained," he said.

In the interview where he made the controversial remark on Carson's faith, Trump contrasted the Seventh-day Adventist Church with his Presbyterian Church, which he described as "middle of the road."

Trump's mention of Carson's faith became a blessing in disguise for the Seventh-day Adventist Church, which received a free publicity boost.

Right after Trump spoke, the Seventh-day Adventist Church put up a website called whoareadventists.org to answer the question: "Who are the Seventh-day Adventists?"

"We are a mainstream Protestant church with approximately 19 million members worldwide and more than one million members in North America. Our doors are always open to the community and to anyone who wishes to worship in one of our more than 6,200 Seventh-day Adventist congregations in North America," the church said on its website.

"I think this is a great opportunity for us," added Daniel Weber, an Adventist spokesman. "Donald Trump did a great thing when he said, 'Who are Adventists?' Now we're answering that question."