Afghan President Hamid Karzai's main election challenger said Sunday that he will withdraw from a planned Nov. 7 runoff, casting new doubts on the legitimacy of the Afghan government as the Obama administration debates U.S. strategy in the region.

As a U.N.-backed commission neared a decision Friday on allegations of fraud in Afghanistan's presidential vote, media reports indicated a runoff may be likely between President Hamid Karzai and second-place finisher Abdullah Abdullah.

Voter participation in a run-off election Friday, with only longtime President Robert Mugabe running, was reportedly light at many polling stations. Some of those who did vote said they were coerced -- fearing punishment or even death.