In the latest blow to Afghanistan's much maligned election, the United Nations-backed commission investigating allegations of fraud has ordered that ballots from 83 polling stations be excluded from the final tally.

The ruling amounts to the highest-profile acknowledgement so far that fraud such as ballot-box stuffing occurred in the election on Aug. 20.

Under the decision issued Thursday by the Electoral Complaints Commission, all ballots from 51 polling stations in Kandahar, 27 in Ghazni and five in Paktika provinces will be cancelled.

In total, the commission has received more than 2,800 complaints regarding the presidential poll and the vote-counting process. More than 700 are considered serious enough to affect polling station results.

The election has been blemished by increasing reports of voting irregularities. Large numbers of polling stations had more than 100 per cent turnout, according to a U.S. monitoring group. President Hamid Karzai's top challenger, Abdullah Abdullah, has accused him of "state-engineered" fraud.

Former Canadian deputy prime minister John Manley, who was one of the international election observers in Afghanistan for the election, recently said the vote was far from being a "free and fair" process.

The decision to exclude the ballots -- considered final under Afghan's election law -- amounts to a more severe ruling than a recount, in which those ballots would eventually be included.

On Tuesday, election officials said that results from 92 per cent of polling stations showed Karzai with 54.1 per cent of the vote, well ahead of Abdullah's 28.3 per cent.

However, many of the affected polling stations are in areas where Karzai enjoyed strong support. If enough of his votes are excluded, his lead could be reduced to below the 50 per cent mark. That would force a presidential runoff.

The complaints commission has ordered audits or recounts at any polling station across the country where more than 100 per cent of voter turnout was recorded, or where a single candidate won greater than 95 per cent of the vote.

Nuristan, Paktia, Helmand and Badghis provinces documented instances where that happened, according to the Washington, D.C.-based National Democratic Institute.

The polling stations with greater than 100 per cent turnout were all in rural areas where voter turnout was expected to be low due to high risk of Taliban attack. Few international observers monitored the areas for the same reason.

On election day, dozens of people were killed by rocket, bombings and attacks on polling stations.

Officials have said they expect to release full election results on Saturday. However, the results won't be declared official until all fraud complaints have been investigated and any re-counts have been completed.