A UN-backed fraud commission threw out votes from 83 polling stations and ordered recounts at hundreds of others in three provinces that form Afghan President Hamid Karzai's political base, reducing his chances of avoiding a runoff. The ruling Thursday was the first time the commission has flexed its muscles in the aftermath of an Aug. 20 presidential election marred by allegations of ballot stuffing, phantom polling stations and turnout at some polls that exceeded 100 percent of registered voters. In an interview with The Associated Press, Karzai's chief challenger, former foreign minister Abdullah Abdullah, charged that the massive scale of what he called "state-engineered" fraud has become clear only as the numbers have trickled out over the past three weeks. With results in from 92 percent of the country's polling stations, Karzai has 54 percent of the vote, according to the latest official count. That's enough to avoid a runoff election with Abdullah, who has 28 percent. But if the UN-backed Electoral Complaints Commission invalidates enough votes, Karzai's margin could drop below 50 percent, forcing him to face Abdullah one-on-one in a second round of voting. Decisions by this fraud commission are final under Afghanistan's electoral law. The group - comprised of one American, one Canadian, one Dutch, and two Afghans - is releasing decisions from each province as investigations finish. On Thursday, the commission threw out ballots from 51 polling stations in Kandahar province, 27 in Ghazni and five in Paktika. Although it did not say how many ballots were invalidated, thousands are likely involved. It ordered election officials to recount votes in hundreds of other voting centers across the three districts in the presence of observers, commission members and representatives of the candidates. All three provinces are dominated by voters who, like Karzai, are ethnic Pashtuns and form the president's political base. The Karzai-appointed Independent Election Commission, which is conducting the count, says it has deducted questionable votes from its totals. But that commission's Web site still lists results from one polling center in the Kandahar city of Spin Boldak where Karzai received exactly 3,000 votes, 600 from each of the five polling stations. Statisticians say such uniform results are highly unlikely and evidence of fraud. "Of course there were fears and concerns about the possibility of fraud or rigging," Abdullah told the AP. "But ... when you investigate it, then you see that the whole thing was state-engineered and unfortunately in collaboration with the IEC (Independent Election Commission), in most cases." Abdullah said he expects that, once the fraudulent ballots are excluded, Karzai's margin will drop below 50 percent, triggering a runoff. There are about 770 polling states still being counted in Kandahar, according to the IEC Web site, meaning the 51 thrown out in the province represent about 5 percent of voting sites. But the fraud commission has ordered audits and recounts of every vote cast in three of Kandahar's province's 17 districts, as well as more than a dozen additional polling stations in Paktika and Ghazni. Investigators examined only a portion of the ballots in voting centers where there were complaints. In Kandahar's Shorabak District they examined 15 out of 41 polling stations. Officials found evidence of ballot stuffing in every one they looked at. In Spin Boldak, investigators found "clear and convincing evidence of ballot stuffing" in 17 of 27 polling stations checked, resulting in the invalidation of more than 6,000 ballots. The commission ordered a recount and audit of all the remaining 354 polling stations in the district. A top official with the IEC, the Karzai-appointed Afghan election commission, has said that recounting ballots at so many polling sites could take months. That raises the question of when a second-round election could even be held, given Afghanistan's harsh winters. Some Western officials have floated a national unity government led by Karzai as a way to ease the electoral crisis and avoid a potentially messy runoff. But Abdullah ruled out that possibility Thursday, telling the AP that he would not accept a position in a new Karzai government. "At this stage one has to focus on the credibility of the process and how to help the process survive," Abdullah said. "The process survives when the fraudulent results are taken out and ... the outcome is decided based on real results rather than fraudulent votes." Asked if that meant no, Abdullah loudly spelled out his response: "N-O." Throwing out ballots is a more severe step than ordering a recount, in which some or all votes could eventually be included in the count. The 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-based National Democratic Institute said its analysis of results found large numbers of stations with more than 600 votes - the maximum number of ballots they are supposed to receive - in Nuristan, Paktia, Helmand and Badghis provinces, along with others. These areas were considered among the most dangerous places to vote, and anecdotal accounts of nearly empty polling stations suggested low voter turnout. Few international observers went to these areas because of security risks. Many voters are thought to have avoided the polls because of Taliban threats and attacks. Dozens of people were killed in rocket bombardments, bombings and polling station raids.