Republicans and African Americans in North Carolina were united in supporting a constitutional ban on gay marriage. The North Carolina is a key swing state in the 2012 presidential election.

North Carolina voters on Tuesday approved a state constitutional amendment that bans same-sex marriage and civil unions, dealing a blow to efforts across the United States to expand gay marriage rights.

The amendment, which says marriage between a man and a woman is the only legally recognized domestic union in the state, passed by a wide margin. With 95 of 100 counties' results reported, about 61 percent of votes backed the amendment.

North Carolina law already blocks gay and lesbian couples from marrying, but the state now joins the rest of the Southeast states in adding the prohibition to its constitution.

RECOMMENDED: Six ways states handled gay marriage

Many voters simply viewed the amendment as a vote on same-sex marriage despite efforts by the measure's opponents to broaden the discussion, said Tom Jensen of the Raleigh-based Public Policy Polling firm.

'Anytime in North Carolina you have a majority of Republicans and African Americans on the same side of an issue, that's a very potent combination,' Jensen said.

Twenty-eight other state have voter-approved constitutional bans on same-sex marriages, according to the National Conference of State Legislatur.