At the same time, envoys were urging both candidates to strike a deal to end the country's election crisis rather than actually going forward with a potentially divisive and costly second vote.
The Aug. 20 poll was marred by charges of ballot-stuffing and voter coercion, mostly to Karzai's benefit. The fraud decisions
- set to be announced as early as Saturday - could force a runoff between him and top challenger Abdullah Abdullah.
Both candidates deny they are negotiating to avert a second round. Karzai's camp is adamant he has won the first round outright, while Abdullah says a runoff is assured.
U.N. Secretary-General Ban Ki-moon, U.S. Secretary of State Hillary Rodham Clinton and British Prime Minister Gordon Brown called the candidates Friday as concerns grew over who will lead the country, and when.
The talks are focused on getting Karzai to accept rulings showing a probable second round, an international official familiar with the discussions said.
The political crisis, and rising U.S. casualties in the war against insurgents, have prompted the Obama administration to review its entire Afghanistan war strategy. Three American troops died in bomb attacks in the south and east, the latest casualties reported by NATO forces Saturday.
The French Foreign Ministry called on all parties to respect results of the fraud investigation and work toward either Karzai's inauguration or preparations for a runoff.
French Foreign Minister Bernard Kouchner, U.S. Democratic Sen. John Kerry and former U.S. ambassador to Afghanistan, Zalmay Khalilzad, were in Kabul on Saturday.
Kerry's trip was planned before the electoral crisis, but he has met with both candidates "to speak for Washington about the need for a legitimate outcome," according to a U.S. Embassy official in Afghanistan. The official spoke anonymously because the U.S. was not formally commenting on the discussions.
Khalilzad held talks with both candidates this week and said he pressed them to reach a solution quickly, noting that U.S. support was not a guarantee if Afghanistan is seen as a hopeless case.
"I urged them to recognize the gravity of the circumstances and to rise to the occasion," Khalilzad said late Friday.
Preliminary election results had put Karzai in the lead with 54.6 percent of the vote, compared with about 28 percent for Abdullah. The results from the fraud investigation could eliminate enough Karzai votes to push him below the 50 percent threshold to force a second round.
Nellika Little, a spokeswoman for the U.N.-backed Electoral Complaints Commission investigating cheating, said the panel hoped to release its decisions later Saturday. Results have already been delayed multiple times.
International diplomats have been urging Karzai and Abdullah to consider a power-sharing arrangement to avoid a runoff that would have to be held within the next few weeks, according to a Western official familiar with the talks.
Karzai is likely to win a second round, but holding it would be a tough challenge because of security concerns and winter snows that could block northern roads and prevent voters from reaching polling stations.