A UN-backed commission found "convincing evidence" of fraud Tuesday in Afghanistan's presidential election and ordered a recount of suspect ballots in at least three provinces, a process that could take months. At the same time, Afghan officials released new returns that give President Hamid Karzai 54 percent of the vote , enough to avoid a run-off unless large numbers of tainted ballots are ultimately thrown out. The separate announcements from the complaints commission, which is dominated by UN-appointed Westerners, and the election commission, which is filled with Karzai appointees, could set the stage for a showdown. The image of a crooked Afghan president rigging the vote threatens to discredit the entire US-led mission here at a time when NATO casualties are mounting and American, European and Canadian voters are fatigued and disenchanted with the war. "The perception of fraud will shorten the length of time that one can expect foreign support," said Ronald E. Neumann, a former US ambassador to Afghanistan. "People will just get disgusted. They'll say, `Why do I sacrifice my son for a leadership that cannot rally the country fairly?'" Four more US troops were killed Tuesday during what the military labeled a "complex attack" in eastern Kunar province. August was already the deadliest month of the eight-year war for both U.S. troops and the entire NATO force at the hands of a resurgent Taliban in southern Afghanistan. President Barack Obama is facing increasing resistance to the war at a time when he has little political capital to spare, and many supporters are urging him to scale back the US presence in Afghanistan. Obama ordered 21,000 additional troops to the country this year with the immediate goal of ensuring a safe and credible election, and Gen. Stanley McChrystal will soon ask him to send thousands more. Those favoring an increased US presence argue that the American troop buildup has not been given enough time to succeed. Also in need of much more time is the process of sorting out the many allegations of vote fraud. State Department spokesman Ian Kelly said Tuesday it could take months - but that the most important thing is for the allegations to be addressed in a way that gives ordinary Afghans confidence in the legitimacy of the outcome. New results released Tuesday gave Karzai more than 50 percent of ballots cast for the first time since officials began releasing partial returns following the Aug. 20 vote. With results in from almost 92 percent of the country's polling sites - representing 5.7 million votes - Karzai has 54.1 percent, and will likely finish the preliminary count with a majority. The standing of top challenger Abdullah Abdullah has dropped dramatically as more results have come in from the south - Karzai's stronghold - in recent days. Abdullah now has 28.3 percent. If, as expected, the Afghan election commission soon announces that a final count shows Karzai won a majority of the vote, the UN-backed Electoral Complaints Commission will begin its investigations of fraud. The commission took its first step in that direction Tuesday, ordering a recount at polling stations where it had found "clear and convincing evidence of fraud." Daoud Ali Najafi, chief electoral officer of the Afghan-run election commission, said recounting votes could take "two months or three months." Afghanistan's electoral law gives the UN-backed complaints commission broad authorities. It can nullify any votes it deems fraudulent, order a re-count of votes or order a new vote entirely. The commission is made up of one American, one Canadian and one Dutch national - all appointed by the UN - and two Afghans appointed by an Afghan human rights organization and the country's Supreme Court. The UN commission did not indicate how many polling stations would require re-counts, but said it had so far identified some with questionable results in Ghazni, Paktika and Kandahar provinces - all southern areas dominated by Karzai's ethnic Pashtun group. If it voids huge blocks of votes in the south, that could drop Karzai's total below 50 percent and force a run-off with Abdullah - a contest which Karzai would be favored to win. The commission said it was also launching investigations in other provinces after receiving more than 720 major fraud complaints throughout the country. The results announced Tuesday do not include potentially tainted ballots that the Afghan-run commission had already quarantined from more than 600 of the country's 26,000 polling stations. The U.N.-backed commission will investigate and determine whether they can be counted or be discarded. Western officials say ballots have been submitted from hundreds of fake voting sites, especially in the south. The Afghan-run commission has tallied dozens of voting sites where Karzai won neatly rounded blocks of ballots - 200, 300 and 500 votes - results that one Western official labeled "illogical." It was unclear whether they were among the ballots that the Afghan commission has set aside. Polling stations showing 100 percent turnout or with a candidate receiving more than 95 percent of the vote will need to be audited and recounted, the UN-backed commission said. Stations with fewer than 100 ballots will be exempt. Grant Kippen, chairman of the complaints commission, said other irregularities include ballots not being folded - meaning they would not fit in a ballot box slot - identically marked ballots and overly large counts. Kippen said he saw a box with 1,700 ballots in Kandahar, even though the maximum should be 600. Although Karzai was practically the toast of the Bush administration, US-Afghan relations cooled significantly when Obama came to office in January. The Afghan leader has angered Washington by pardoning drug dealers and cozying up to warlords, actions that he evidently thought were necessary to ensure his re-election. It would now appear that those very same Afghan power brokers have fueled the hundreds of apparent incidents of fraud to help re-elect Karzai and thereby retain the patronage jobs and other benefits they've reaped by allying themselves with his government.