LOS ANGELES (AFP) – A Republican official in California has apologized for sending an email containing a picture depicting US President Barack Obama as a chimpanzee.

The family portrait-style image of three chimps had Obama's head on the body of a baby chimp with the message "Now you know why no birth certificate," in reference claims among some Republicans that Obama wasn't born in the United States.

Civil rights groups expressed shock that Marilyn Davenport sent what they said was an offensive image of America's first black president.

The state chapter of the National Association for the Advancement of Colored People called on Davenport to resign from the Orange County Republican Central Committee.

"To my fellow Americans and to everyone else who has seen the email I forwarded and was offended by my action, I humbly apologize and ask for your forgiveness of my unwise behavior," said Davenport, who also active in the conservative Tea Party movement.

"At the time I received and forwarded the email, I didn't stop to think about the historic implications and other examples of how this could be offensive."

Davenport's statement made several references to Biblical passages. She said she's an "imperfect Christian lady who tried her best to live a Christ-like honoring life" and that she would "never do anything to intentionally harm or berate others regardless of ethnicity."