KABUL: The U.N.-backed commission investigating fraud in Afghanistan's election issued its first orders Thursday 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 has 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.

Decisions by the commission are final under Afghanistan's electoral law. The group is releasing decisions from each province as investigations finish. The U.N.-backed commission is comprised of one American, one Canadian, one Dutch, and two Afghans.

International censure of the vote has increased since Tuesday, when election officials released preliminary results from 92 percent of polling stations showing Karzai with 54.1 percent, far ahead of top challenger Abdullah Abdullah, who had 28.3 percent. Tuesday's partial results were the first to show Karzai surpassing the 50 percent threshold needed to avoid a runoff.

Election officials have said they expect to release full results Saturday, but these will not be deemed official until all fraud complaints have been investigated and any re-counts are finished.

The complaints commission ordered an audit and recount countrywide of stations where turnout was at or above 100 percent, or where one candidate won more than 95 percent of the vote.

The Washington, D.C.-based National Democratic Institute said its analysis of results found large numbers of stations with more than 600 votes — the 100 percent mark — in Nuristan, Paktia, Helmand and Badghis provinces, along with others.

These are areas considered some of the least secure on polling day and in which anecdotal accounts of nearly empty polling stations suggested low voter turnout. Few international observers went to these areas because of security risks.

Though there are no official turnout figures from the Aug. 20 poll, government officials and independent observers have generally said voters showed up only in low numbers because of Taliban threats ahead of the vote and attacks on election day.

Dozens of people were killed amid rocket bombardments, bombings and polling station raids.

The monitoring group said it had "deep concern" over the high levels of fraud complaints pouring in. The Electoral Complaints Commission has received more than 2,800 complaints about polling day and the counting process, of which 726 have been deemed serious and specific enough to affect polling station results.

"It will be impossible to determine the will of the Afghan people," unless fraud complaints are thoroughly investigated, it said in a statement.

The group had more than 100 international and Afghan observers in 19 of Afghanistan's 34 provinces. It did not have observers in many of the provinces where it saw problems in the results, but the figures have been posted on the Web.

Election officials have said they are holding back suspicious results, but they appear to be using a different metric than the separate complaints commission because voting center results in which candidates won more than 95 percent of the vote have been posted, along with stations that have tallies higher than 600.

The National Democratic Institute says it is a nonpartisan organization aimed at strengthening democratic institutions. It is funded partly by private donations and the U.S. and other governments.