Senior sources say top international figures have been working to persuade President Hamid Karzai that he may have to face a second round of voting.
A fraud investigation is expected to bring Mr Karzai's vote tally below the 50% needed to avoid a run-off.
Officials say Mr Karzai is furious over the prospect of facing a second round.
The fraud allegations which have surfaced in the two months since the 20 August poll have generated huge political uncertainty, reports the BBC's Martin Patience in Kabul.
It comes at a time when Washington is debating whether to send more troops.
Fraud findings
Mr Karzai was initially awarded 55% of votes in the poll, with his nearest rival, Abdullah Abdullah, getting 28%.
AFGHAN FRAUD ALLEGATIONS
13 Oct: Karzai casts doubt on fair functioning of ECC, but his opponents accuse him of manufacturing his concerns
30 Sep: UN recalls envoy Peter Galbraith following row over the vote recount process
15 Sep: ECC chief says 10% of votes need to be recounted
8 Sep: IEC says votes from 600 polling stations "quarantined"
3 Sep: Claims 30,000 fraudulent votes cast for Karzai in Kandahar
30 Aug: 2,000 fraud allegations are probed; 600 deemed serious
20 Aug: Election day and claims 80,000 ballots were filled out fraudulently for Karzai in Ghazni
18 Aug: Ballot cards sold openly and voter bribes offered
Election: Main fraud allegations
But the UN-backed Electoral Complaints Commission (ECC) is due to report its findings into fraud allegations this weekend.
It will report to the Independent Election Commission (IEC), which could adjust the final tally based on the report - bringing Mr Karzai's vote total below 50%, and triggering a run-off.
US Secretary of State Hillary Clinton and British Prime Minister Gordon Brown telephoned the candidates on Friday.
Senior sources told our correspondent they had urged Mr Karzai to accept the findings of the ECC's fraud investigations.
The French Foreign Minister Bernard Kouchner and US Senator John Kerry - chair of the US Senate's foreign relations committee - are also in Kabul meeting Mr Karzai and Mr Abdullah.
Karzai 'fury'
Mrs Clinton told CNN: "It is likely that they will find that President Karzai got very close to the 50-plus-1" (50% of votes, plus one vote) threshold for a second round of voting.
She added: "I think one can conclude that the likelihood of him winning a second round is probably pretty high."
But officials told our correspondent that Mr Karzai is furious at the turn of events, and is threatening to delay - or even block - attempts to hold a second round.
His position appears to have been strengthened by the IEC. Its spokesman said that not all the findings of the investigation may be implemented - despite the fact that the IEC is constitutionally bound to obey the orders of the ECC.
Their reported confrontation may delay the official announcement of results - providing a breathing space for the frenzied diplomatic efforts, unnamed diplomats have told news agencies.
Strategy review
A run-off between Mr Karzai and Mr Abdullah would be due within two weeks, although security concerns and winter snows could hamper efforts.
The US is reviewing its strategy in Afghanistan.
Three American soldiers were killed in bomb attacks in the country as Nato-led forces fought Taliban militants.
Two of them died in eastern Afghanistan on Friday and one in southern Afghanistan, officials said.
