Afghan officials issued full preliminary results showing President Hamid Karzai received 54.6% of the vote in last month's election, a result that could be annulled by mounting fraud allegations.
European Union election monitors say fraud is indicated in more than a quarter of the 5.6 million votes counted.
The August 20 vote has been so tainted by reports of ballot-box stuffing and questionable tallies that many expect final results - once fraudulent ballots are thrown out - to vary widely from the preliminary count now released.
If enough votes are thrown out for Karzai to drop below 50%, it will force him into a two-man runoff with top challenger Abdullah Abdullah, a former foreign minister who has 27.7% of the vote.
The preliminary count gave Karzai 3.1 million votes to Abdullah's 1.6 million.