Afghan President Hamid Karzai casts his vote at a polling station in Kabul last week. (Rafiq Maqbool/Associated Press)Incumbent Afghan President Hamid Karzai has increased his lead over his main challenger in the country's elections with 44.8 per cent of the vote after 17 per cent of the polls have been tallied, the electoral commission said Wednesday.

Abdullah Abdullah, the former foreign minister and top challenger, has 35.1 per cent of the vote, an official from the commission told reporters in the Afghan capital, Kabul.

The commission plans to release partial results each day for the next several days. Final results won't be made public until mid-September or later in the month.

Karzai needs a simple majority of more than 50 per cent to avoid a second-round run-off.

Vote-rigging alleged

The partial results come after low voter turnout last week and amid allegations of fraud and fears of more post-election violence.

Abdullah has accused Karzai and his supporters of widespread rigging, including ballot stuffing and voter intimidation. Karzai's side has denied the allegations.

The election was held during the most violent summer in Afghanistan since the 2001 U.S.-led invasion.

The Taliban threatened to disrupt last week's vote through violence and vowed to chop off the ink-stained fingers of those who cast ballots.

On Tuesday, a large blast made by five car bombs strung together rocked Kandahar city, killing at least 43 people, wounding 65 and damaging dozens of buildings, officials said.

On Wednesday, a purported Taliban spokesman denied the militant group was responsible for the attack.

NATO also announced the deaths of two U.S. soldiers on Wednesday in separate attacks in southern and eastern Afghanistan.