Palin ducks out of US presidential race

"After much prayer and serious consideration, I have decided that I will not be seeking the 2012 GOP nomination for President of the United States," Palin writes. "I believe that at this time I can be more effective in a decisive role to help elect other true public servants to office - from the nation's governors to congressional seats and the presidency."

Background - who is Sarah Palin?

She promises to "help coordinate strategies to assist in replacing the president, retaking the Senate, and maintaining the House [of Representatives]".

Palin, a darling of the ultra-conservative Tea Party movement, had kept speculation about her presidential ambitions ticking over with a "One Nation" bus tour through crucial early-voting states.

But her opinion poll ratings made it seem unlikely that she could win.

Her decision came the day after New Jersey Governor Chris Christie pulled out of the race and leaves an expected two-way battle for the nomination between former Massachusetts governor Mitt Romney and Texas Governor Rick Perry, although former pizza company executive Herman Cain gaining ground.

With incumbent Barack Obama seen as vulnerable due to the faltering economy and high unemployment, Republicans need a candidate who can rally the conservative base but who can attract floating voters.