Hamid Karzai, the incumbent in Afghanistan's presidential poll, has widened his lead with 42 per cent of the vote as partial results of last week's election continue to trickle in.

Abdullah Abdullah, his main challenger and a former foreign minister, was trailing with 33 per cent as Karzai inched closer to the 50 per cent threshold that would allow him to avoid a run-off.

Coming in a distant third was Ramazan Bashar-dost with 11 per cent, while the rest of the votes were shared among the remaining candidates.

Karzai had 422,137 votes with Abdullah on 330,751 votes, the Independent Election Commission (IEC) said after releasing results from 17 per cent or nearly a million of counted ballots on Wednesday.

The race between the two increasingly bitter rivals has been tainted with claims of fraud and ballot box-stuffing, most of it in favour of Karzai, whose camp has been claiming victory since shortly after polls closed.

The first results released from last week's ballot had put Karzai neck and neck with Abdullah, who led a strong campaign for change and has alleged that widespread state engineered fraud has damaged the vote.

Earlier James Bays, Al Jazeera's correspondent in Kabul, said Abdullah had lost his position a little but added that the situation could change when more than half of the ballots are counted by the weekend.

Afghan election officials said the final tally will be known only in September [AFP]

The second-ever direct presidential election has been marred by Taliban attacks and simmering ethnic tension.

Already, 2009 has become the deadliest year for foreign troops since the US-led invasion eight years ago.

On Tuesday a massive bombing in Kandahar city in the south killed at least 43 people and injured 65 others in what has become the deadliest attack in over a year.

Analysts have said that a low voter turnout, one of the aims of the Taliban intimidation campaign, could raise questions about the legitimacy of the victor, and increase fears of unrest.