KABUL — The U.N.-backed commission investigating fraud in Afghanistan's election issued its first orders today to exclude some ballots from the final tally, throwing out votes from 83 polling stations in areas of strong support for President Hamid Karzai.

The Aug. 20 poll has been increasingly marred by reports of ballot-box stuffing and suspicious tallies. A U.S. monitoring group said "large numbers of polling stations" had more than 100 percent turnout and President Hamid Karzai's top challenger has accused him of "state-engineered" fraud.

Karzai currently has more than 50 percent of the preliminary vote count. But if the commission throws out enough votes, he could drop below 50 percent and be forced into a run-off.

The Electoral Complaints Commission threw out ballots at 51 sites in Kandahar, 27 in Ghazni and five in Paktika. All three provinces are dominated by ethnic Pashtuns and are areas where Karzai, also an ethnic Pashtun, would expect to do well.

The commission did not say how many overall votes were nullified.

Throwing out ballots is a more severe step than ordering a recount, in which the votes could eventually be included. The commission also ordered some votes to be recounted in Ghazni.