KABUL, Afghanistan - An investigation of alleged fraud in Afghanistan's presidential election was winding down Wednesday, officials said, with no indication that it could overturn a win for U.S.-backed interim leader Hamid Karzai.

The results of the probe, and a declaration that Karzai has won a five-year mandate, are expected to be announced over the weekend.

Officials declared counting from the Oct. 9 poll complete on Tuesday. By Wednesday, a tally of 99.6 percent of the votes gave Karzai 55.4 percent, enough for an outright victory without a run-off.

A member of a panel of foreign experts set up to look into fraud allegations leveled by Karzai's challengers said the panel had begun drafting its report.

Several candidates have said they will accept their defeat once irregularities are officially acknowledged.

"We hope (the candidates) will accept the findings," said Craig Jenness, a Canadian lawyer on the three-man panel. "They're not giving us any indication that they would not."

Foreign observers have judged the election as flawed, but fair in its outcome. Karzai, a Pashtun tribal leader, was the only candidate to win important backing from beyond his ethnic kin, though he suffered stinging defeats in some northern and central provinces.

After the vote, the three-member panel and the joint U.N.-Afghan electoral commission quarantined about 500 suspect ballot boxes.

Officials say there was clear evidence of ballot-stuffing, and that some boxes will likely be excluded from the vote. But all but a handful of boxes had been cleared by Wednesday evening, indicating the problems were considered minor.

Karzai is due to be sworn in in about a month for a five-year term as Afghanistan's first popularly elected leader.

An estimated 8.2 million ballots were cast in the historic vote, a turnout of about 70 percent, which U.S. and Afghan officials hailed as a nail in the coffin of the Taliban.

Militant threats to disrupt the vote proved largely hollow, although an attack on an American military convoy on Wednesday provided a reminder of the tenacious insurgency.

Three American troops and an Afghan soldier were injured when a bomb exploded near their Humvee in southeastern Qalat province, the military said. None suffered life-threatening injuries.

In another incident, U.S.-led forces killed an "enemy person" in an operation near the Pakistani border, the American military said.

An Afghan official identified the victim as Janat Khan, a local man, and said he was killed overnight during a raid on an office in Khost.

American spokesman Maj. Mark McCann gave no information on why the man was targeted. "I can only say that the forces who conducted the operation knew what they were doing."