President Hamid Karzai's leading challenger accused him of using the Afghan state to "rig" this week's election and has made detailed allegations of cheating by government officials.
Abdullah Abdullah, once Karzai's foreign minister, said he was in contact with other campaigns to explore the possibility of a coalition candidacy in case none of the 36 candidates won enough votes in last Thursday's ballot to avoid a runoff, probably in October.
The accusations, which Karzai's spokesman denied, are the most direct Abdullah has made against the incumbent in a contest that likely has weeks to go before a winner is proclaimed. Both Abdullah and Karzai claim they are in the lead based on reports from campaign pollwatchers monitoring the count.
Officials of Abdullah's campaign have alleged fraud in several southern provinces where the insurgency is strongest and Karzai had been expected to run strong.
"He uses the state apparatus in order to rig an election," Mr Abdullah said. "That is something which is not expected."
Mr Abdullah said it "doesn't make the slightest difference" whether Karzai or his supporters ordered the alleged fraud.
"All this happens under his eyes and under his leadership," Mr Abdullah said. "This is under his leadership that all these things are happening, and all those people which are responsible for this fraud in parts of the country are appointed by him. And I'm sure he has all those reports, so he knows all of this. This should have been stopped and could have been stopped by him."
If Mr Abdullah supporters believe the election was stolen, it could lead to the type of street violence that marred Iran's presidential election in June. Mr Abdullah has called for calm and says grievances should be resolved through the country's Electoral Complaints Commission.
He alleged that government officials in Kandahar and Ghazni provinces, including a provincial police chief and a No. 2 provincial election official, stuffed ballot boxes in Karzai's favor in six districts. He also said his monitors were prevented from entering several voting sites.
Mr Karzai's campaign spokesman Waheed Omar dismissed Mr Abdullah's allegations and claimed the president's camp had submitted reports of fraud allegedly committed by Abdullah's followers to the election complaint commission.
"These are not new allegations. These were made even before the election took place," Mr Omar said. "We have documented violations that were made by Abdullah's campaign team. But we believe our job is to report to the elections complaint commission ... We do not want to make a media propaganda campaign out of the violations we have documented."
Mr Omar said losing candidates often claim fraud to "try to justify their loss."
Millions of Afghans voted in the country's second-ever direct presidential election, although Taliban threats and attacks appeared to hold down the turnout, especially in the south where Karzai was expected to run strong among his fellow Pashtuns. Election observers have said the voting process was mostly credible, but are cataloging instances of fraud and violence.
Mr Abdullah said he was not claiming victory but "in these early days and early preliminary results I'm very happy."
US, UN and Afghan officials said they had not expected a fraud-free election, but hoped that cheating would be on a small enough scale that the vote was seen as credible.
An Afghan monitoring group, the Free and Fair Election Foundation of Afghanistan, said Saturday that its observers saw widespread problems from election officials who were not impartial and were pressuring people to vote for certain candidates. Election monitors also reported seeing voters carrying boxes of voter cards — so that multiple votes could be cast — to polling sites and saw many underage voters, according to the foundation head Nader Nadery.
The National Democratic Institute, a US-based democratic group, said Saturday the vote "involved serious flaws" and pointed to the fact that members of the Independent Election Commission are appointed by Mr Karzai, suggesting a likelihood of bias.
Preliminary results will not be released until Tuesday, but final certified results won't come until next month. If neither Karzai or Abdullah gets 50 per cent of the vote among a field of some three dozen candidates, then the two will go to a run-off.
Anticipating that likelihood, Abdullah said he has been in contact "either directly or indirectly" with most of the presidential candidates — aside from Mr Karzai — over the possibility of a coalition candidacy in round two.
If Mr Abdullah could persuade supporters of Ramazan Bashardost and Ashraf Ghani — the other top candidates — to endorse him, the extra support could be enough to defeat Karzai in a second round.
Taliban militants carried out dozens of attacks on election day, violence that killed 26 Afghan civilians and security forces. Abdullah said he had expected better security and more competence from the election authorities.
In a harrowing attack on voting day, Taliban militants cut off the ink-stained fingers of two voters in Kandahar province shortly after casting ballots, said Nadery. Kandahar is the spiritual birthplace of the Taliban.
Rumours that militants would sever voters' ink-stained fingers spread before the vote. A Taliban spokesman had said militants would not carry out such attacks, but the Taliban is a loose organization of individual commanders who could make good the threat on their own.
Also Saturday, the US command reported that an American service member died of a noncombat injury in eastern Afghanistan. No further details were released. The death brought to 35 the number of U.S. service members to die in Afghanistan this month.