KABUL, Afghanistan (CNN) -- Afghanistan's Independent Election Commission said Sunday it was tossing ballots from 447 polling stations in figuring results of the August presidential election.
Afghan children stand in front of a billboard of President Hamid Karzai in Kabul on Sunday.
The number of votes thrown out was not immediately known, but it could be as many as tens of thousands.
The IEC has sought to reassure voters of its impartiality and transparency in tallying the results of the election, mainly responding to accusations by Abdullah Abdullah.
Abdullah is the main challenger to Afghan President Hamid Karzai, who is seeking a second term in office. Abdullah is Karzai's former foreign minister.
As of Sunday, 74.2 percent of the votes had been tallied, the IEC said. Karzai had 48.6 percent of the vote, with Abdullah at 31.7 percent. More than 153,000 votes had been declared invalid, but it was not known whether that number included votes from the 447 polling stations. Watch a report on alleged election fraud »
"The IEC has been completely impartial and neutral in its activities and in fulfilling its duties throughout the process," said IEC head Daoud Ali Najafi on Sunday.
Karzai needs 50 percent of votes to avoid a runoff.
Abdullah has called the alleged vote rigging "state-engineered fraud." He is demanding that the IEC stop announcing vote tallies from the provinces, and that the Electoral Complaints Commission inform Afghans about the status of its investigations.
By September, Afghanistan election officials said they had received nearly 2,500 complaints, with about 560 of them deemed serious enough to potentially affect the outcome of the race. The grievances include polling irregularities, voter intimidation and ballot stuffing.
The complaints commission said that in order for election results to be certified, it must resolve the complaints it has received.
CNN's Atia Abawi and Ingrid Formanek contributed to this report.