KABUL: Two months after Afghans voted in controversial presidential elections, electoral authorities are expected to announce on Saturday if they have a winner or if another poll is needed.

Officials in Kabul dismissed a US media report that a run-off will be called as President Hamid Karzai's share of the vote had dropped below the 50-percent victory threshold with the cancellation of fraudulent ballots cast for him.

But they said that Afghan politicians and their international backers have been involved in days of vigorous horse-trading in the hope of averting a run-off, which many fear could further destabilise the fragile country.

Afghanistan's August 20 election has been overshadowed by allegations of fraud, mostly against Karzai, including findings by EU observers that a quarter of all votes, or 1.5 million, were suspicious.

Karzai leads preliminary results with around 55 percent of the vote. He needs 50 percent plus one vote to be declared the winner.

His main rival Abdullah Abdullah has around 28 percent.

An official announcement is to be made by the Independent Election Commission (IEC), widely regarded as pro-Karzai, which acts on the orders of the UN-approved Electoral Complaints Commission (ECC).

The ECC should send its order, based on the findings of investigations into ballot-stuffing allegations, to the IEC on Saturday, an ECC source told AFP, adding that the IEC is constitutionally bound to obey.

But some officials expressed concern late Friday that the two bodies were still wrangling over details, which could delay the IEC's announcement.

The Washington Post reported that Karzai's share of the vote had dropped to 47 percent after thousands of suspicious ballots were investigated by the ECC.

"There is no way anyone can make that prediction and stand it up, it is just so close," said a Western diplomat familiar with the process.

"Karzai is hovering around 50 percent and the feeling is that he could just clinch it."

This week has seen international efforts to broker a deal between Karzai and Abdullah to avoid both a run-off and any outbreak of violence.

Influential visitors to Kabul included the Aga Khan, leader of a minority Islamic sect and one of the world's wealthiest men, whom one European diplomat described as the biggest single aid donor to Afghanistan.

His followers account for about six percent of the national vote.

Former US ambassador to Iraq and Afghanistan, Zalmay Khalilzad, met Karzai and Abdullah in what diplomats interpreted as an effort to bind the two into a coalition government.

Khalilzad told reporters that "Afghan leaders" had been urged "to recognise the importance of the moment and seize it" as Western governments debate their continued military and financial commitment.

"The Afghan people should not assume that the international community will stay here regardless and indefinitely," he said.

Abdullah has said he will not accept a post in a Karzai government if the president is found to have won a new term through corrupt means, but during the week appeared to soften his stance.

Diplomats have said Abdullah has used the election campaign and aftermath to position himself as a future player and that, aged 48, he has a potentially long political career ahead of him.

A Western official familiar with the negotiations said discussions were focusing on whether the Afghan constitution allows a coalition government to be formed to avoid a run-off.

Constitutionally, a second round should be held within two weeks of the announcement, and experts say it would have to be held quickly as winter snows will soon make large parts of the country impassable.

Preparations have been made, with ballot papers printed in London and indelible ink waiting in Kabul to be sent to polling stations.

But there are concerns that a new vote would attract even fewer voters than the first, which saw overall turnout of lower than 40 percent -- five percent in some troubled regions -- after a fearsome Taliban campaign kept people away from polling stations.

Pashtun tribal leaders in the south -- heartland of Karzai's support as well as Taliban influence -- said this week they would not vote a second time because the government had proved itself incapable of providing security.

Some observers see a run-off as the only way to salvage credibility for the election, which has highlighted corruption in Karzai's government as US President Barack Obama mulls whether to send more troops to the country.