DES MOINES — A prominent leader in the Iowa/Nebraska branch of the NAACP — the country’s oldest civil rights group — announced today that he is resigning as branch president and a national board member in the wake of the national organization’s decision to endorse marriage between people of the same gender.

The Rev. Keith Ratliff Sr. of the Maple Street Missionary Baptist Church in Des Moines issued a statement saying he was stepping down from the NAACP national board and as Iowa/Nebraska state conference president “due to the NAACP’s position and support of same-sex marriage.

“I want to thank the NAACP for the privilege to humbly serve in such an organization and thank all those I had the privilege to work with in the states of Iowa, Nebraska and throughout the country,” Ratliff said in the statement. He was unavailable for further comment.

Ratliff has been an outspoken critic of same-sex marriage rights and has spoken at Statehouse rallies seeking an amendment to the Iowa Constitution to undo a controversial, landmark state Supreme Court ruling in April 2009 that gave legal status to civil marriages involving same-gender couples. The proposed constitutional amendment would define marriage in Iowa as only between one man and one woman.

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Earlier this year, the national board of directors of the National Association for the Advancement of Colored People voted to support marriage equality.

During a Statehouse rally in March 2011, Ratliff said his support for traditional marriage was biblically based, adding, “This isn’t a private interpretation, a Burger King religion, and by that I mean a ‘have it your way’ religion.”