US Republican presidential hopeful Mitt Romney has sought to dispel public scepticism about his Mormon faith by promising to defend religious freedom.
Speaking only 28 days before the first nominating race, he said he would serve "no one religion, no one group, no one cause, and no one interest" if elected.
But Mr Romney also criticised those who called for the removal from public life of "any acknowledgement of God".
The former governor of Massachusetts would be the first Mormon US president.
While he trails former New York mayor Rudy Giuliani in the national polls at present, Mr Romney is one of two frontrunners in Iowa, and well ahead of other Republicans in New Hampshire.
These states will host respectively the first caucus and the first primary on 3 and 8 January.
In an address at the library of former US President George HW Bush in College Station, Texas, Mr Romney emphasised the importance of religious freedom in the US.
"If I am fortunate to become your president, I will serve no one religion, no one group, no one cause, and no one interest," he said.
"A president must serve only the common cause of the people of the United States."
Correspondents say Mr Romney's speech recalls one made by John F Kennedy during his successful campaign for president in 1960 in which he discussed his Catholic faith.
Mr Romney stressed that, like Kennedy, he was "an American running for president" who would not define his candidacy by religion.
"There are some who would have a presidential candidate describe and explain his church's distinctive doctrines," he said.
"To do so would enable the very religious test the founders prohibited in the Constitution. No candidate should become the spokesman for his faith."
'Shared moral convictions'
Mr Romney also tried to dispel fears among conservative Christians by stressing that while "differences in theology" existed, he shared "moral convictions" with Americans of all faiths.
"Whether it was the cause of abolition, or civil rights, or the right to life itself, no movement of conscience can succeed in America that cannot speak to the convictions of religious people," he added.
Born 12 March 1947 in Detroit, Michigan
Educated at Brigham Young University and Harvard
Chair of Salt Lake City Olympic Committee, 1999-2002
Governor of Massachusetts, 2003-2007
The former governor also warned that some people had attempted to take the notion of the separation of church and state "well beyond its original meaning" and sought to remove from the public domain any acknowledgement of God.
"Religion is seen as merely a private affair with no place in public life. It is as if they are intent on establishing a new religion in America - the religion of secularism. They are wrong."
While Mr Romney is seen as a frontrunner in the Republican nomination race, polls have suggested that one-quarter to one-third of Americans would not elect a member of the Mormon Church.
Some Christians view the Church of Jesus Christ of Latter Day Saints as a cult, and its image still suffers from being associated with the practice of polygamy, which it banned over a century ago.
The Church has an estimated six million members in the US, where it was founded in 1830 by an American, Joseph Smith.
The BBC's North America editor, Justin Webb, says Mr Romney resisted making this speech for some time, but he has now made his pitch by claiming, in essence, that Americans need not feel uncomfortable.