North Carolina bans gay marriages

The measure was passed by 61% against 39% as of 0230 GMT, according to preliminary results from the North Carolina State Board of Elections.

Similar state constitutional amendments have been approved in some 30 US states.

The amendment solidifies and expands already enacted North Carolina law forbidding same-sex marriage.

President Barack Obama has recently come under greater pressure to clarify his position on gay marriage, after Vice President Joe Biden stressed that he personally was fully comfortable with it.

Money from national interest groups poured into North Carolina ahead of the election - the National Organization for Marriage which opposes gay unions contributed $425,000 to the Vote for Marriage campaign, according to the latest reports.

The Human Rights Campaign contributed some $257,000 to the opposition, the Coalition to Protect All NC Families.

On the other side, former president Bill Clinton and his ex-chief of staff, Erskine Bowles, a North Carolina native, recorded telephone messages to voters urging them to oppose the measure. In a statement, President Barack Obama's campaign also opposed the amendment.

"The passage of Amendment One is a profound injustice. Singling out a class of citizens for discriminatory treatment is unfair, unlawful and violates basic American values," said Adam Umhoefer with the American Foundation for Equal Rights, a leading US group supporting gay marriage, after the vote.

There are now tens of thousands of same-sex couples in several US states and the District of Columbia who are legally married where they live.

A Pew Research Center Survey last month found that 47% of Americans now favor allowing gay couples to marry - well up from 39% in 2008 and 31% in 2004. 43% percent remain opposed.