Major allegations of fraud in Afghanistan's presidential election topped 550 by Sunday, more than doubling the figure investigators reported just two days earlier, officials said. The spike indicates just how pervasive ballot box stuffing and voter intimidation may have been during the country's Aug. 20 vote, threatening the legitimacy of the election. The hundreds of complaints could also greatly delay final results, which cannot be announced until major fraud allegations have been investigated, and are already not expected until mid-September at the earliest. A delay could create a power vacuum in Afghanistan and the volume of allegations could foment violence if people feel they have been cheated. On Sunday, an election official was attacked in the south. Gunmen on motorbikes drove up to the home of the second-highest electoral official in Kandahar province and shot him as he walked out of his front gate to go to work, said Mohammad Samimi, a spokesman for the provincial electoral commission. Sharafuddin, who only goes by one name, was seriously wounded and is being treated in a military hospital, he said. Sharafuddin was the operations manager for the provincial commission, meaning he was in charge of the logistics of how polling stations would operate and how ballots would be handled. Partial results of the vote so far show President Hamid Karzai leading with 46.2 percent of votes, and top challenger Abdullah Abdullah with 31.4 percent. The count is based on votes from 35 percent of the country's polling stations. Karzai will need to reach 50 percent of the votes to avoid a two-man run-off. Polls had favored Karzai to win the election, though not necessarily in a single round. Karzai's popularity has waned in recent years over concerns about corruption and resurgent violence. He also has been criticized for recruiting former warlords to gain the votes they control. One of the most controversial of these, Uzbek warlord Gen. Abdul Rashid Dostum, flew into Afghanistan from Turkey shortly before election day to show his support for Karzai and left late last week, a representative said. 'The purpose of his coming to Afghanistan was to participate in the election and to support Karzai,' said Sayed Noorullah Sadat, the chief of Dostum's political party. Dostum is alleged to have been responsible for the deaths of up to 2,000 Taliban prisoners early in the Afghan war, and U.S. officials were critical of the decision to allow him to return. 'The United States maintains serious concerns about the prospective role of Mr. Dostum in today's Afghanistan,' the embassy said in a statement Sunday. Sadat said Dostum has no immediate plans to return to Afghanistan. Asked if a second round of voting might bring Dostum back, Sadat said it was premature to talk about a runoff with votes still being counted. He added that Turkey is Dostum's home and that Dostum has a medical condition that is easier to treat in Turkey. He did not provide further details. The independent Electoral Complaints Commission has received more than 2,000 allegations of fraud and intimidation on voting day or during the subsequent counting of ballots, said Nellika Little, a spokeswoman for the group. Of those, 567 have been deemed serious enough to affect the outcome of the poll if proved true, Little said. The commission had reported 270 major allegations on Friday. The commission is still evaluating complaints, so the figure could rise further. The widespread fraud allegations have raised concerns about whether Afghans will accept the certified results. Voting day was marred by low turnout amid Taliban threats and attacks. Fraud allegations against Karzai were also raised in the 2004 election. A joint U.N.-Afghan panel found many cases of ballot-box stuffing, but said there was no evidence it was widespread and only favored Karzai. Karzai received 55.4 percent of the votes in the 2004 election -- 39 percentage points ahead of his closest challenger. This time, several presidential candidates have leveled accusations of fraud, including allegations that electoral officials forced voters to cast ballots for certain candidates and marked unused ballots for their candidate after election day. Abdullah and other candidates have produced videos documenting many allegations and Abdullah has charged Karzai of mobilizing state resources to steal the election. Karzai's campaign has denied that and countered by accusing Abdullah's campaign of fraud. Both camps have urged the country to wait for the complaints commission to finish its work. Military operations and violent insurgent attacks have continued in the interim. On Saturday, militants killed a provincial counterterrorism chief in an ambush in eastern Afghanistan. Fayez Khan, who headed counterterrorism operations for Khost province, was driving home in a convoy with police and bodyguards when he was ambushed, said Tahir Khan Sabari, the province's deputy governor. On the same day in Kandahar, three civilians died in the blast of a roadside bomb struck by a police vehicle, said Fazen Mohammad Sherzad, the deputy police chief. Two police officers were wounded but none killed. Afghan and international forces battled insurgents on Friday in eastern Paktika province, killing about three dozen militants, said Capt. Elizabeth Mathias, a spokeswoman for U.S. forces. A NATO statement said the Afghan and international troops also destroyed weapons and a complex of bunkers belonging to the Haqqani militant network, which operates across the Afghan-Pakistan border. No casualties were reported for international or Afghan troops, nor for civilians. ------ Associated Press Writers Rahim Faiez and Amir Shah in Kabul and Noor Khan in Kandahar contributed to this report. 