Early results from the Afghan election showed incumbent President Hamid Karzai in a tight race to return to power, on the same day that five deadly car bombs killed and wounded dozens in Kandahar.

On Tuesday, Afghanistan's Independent Election Commission announced that with 10 per cent of the ballots counted, Karzai and his main challenger, former foreign minister Abdullah Abdullah, have each captured about 40 per cent of the vote.

Karzai is leading, however, with about 40.6 per cent support in the ballots counted so far, versus 38.7 per cent support for Abdullah.

The initial results were based on 524,000 valid votes, the commission said. Another 31,000 votes were thrown out.

If no candidate garners more than 50 per cent of the vote, there will be a runoff.

The commission intends to release more electoral results over the next few days.

But the final, certified results won't be ready until mid-September at the earliest.

The election news came on a day when Kandahar -- the largest city in southern Afghanistan -- was rocked by five car bombs that detonated simultaneously. At least 41 people died and another 64 were wounded.

An Associated Press reporter said the ensuing explosion was the largest he had heard since living in Kandahar for nearly eight years.

The car bombs destroyed the headquarters of a Japanese construction company and caused the collapse of nearby buildings and houses.

Meanwhile, a separate bomb blast in the southern part of Afghanistan killed four U.S. troops. Their names have not yet been released.

Prior to the release of the initial voting results on Tuesday, six presidential candidates warned that allegations of fraud may undermine the legitimacy of the election and potentially spark violence in the country.

"Fraud in the elections could result in increased tension and violence," the six candidates warned in a statement.

Karzai spokesperson Humayun Hamidzada said the Afghan government is confident that it can handle any problems with violence stemming from public reaction to the vote.

"If there are some people who try to violate the situation, I should say that today Afghanistan has its own security institutions, today Afghanistan has its own rules and law" he told reporters gathered for a briefing in Kabul on Tuesday. "If anyone tries to break the law, they will face the legal process."

Fraud complaints

CTV South Asia Bureau Chief Janis Mackey Frayer said that hundreds of complaints have been registered with the country's Electoral Complaints Commission, though some are considered more troubling than others.

"There have been hundreds of complaints so far, more than 800 according to some," she told CTV News Channel during a telephone interview from Kabul on Tuesday. "But of the ones that are deemed serious by the ECC, these are the ones that are thought to have a material impact...These are the ones that are being seriously investigated and that investigation could take weeks."

With 50 complaints deemed serious in nature, University of Waterloo professor Mark Sedra said it appears that the level of fraud was higher than in either of the previous two elections.

"This is something certainly to be concerned about and I think to many it will challenge the legitimacy of the election for many Afghans," Sedra told CTV News Channel during a Tuesday morning interview.

To ensure that both the Afghan and international communities trust the final results, it is necessary that Afghan election officials diligently investigate all serious cases of suspected voting fraud, Sedra said.

Abdullah has alleged that fraud has taken place that favours Karzai, the current president.

"If the widespread rigging is ignored this is the type of regime that will be imposed upon Afghanistan for the next five years, and with that sort of system, a system that has destroyed every institution, broken every law," he said at a news conference that took place before the first results were released.

Karzai has made similar accusations about Abdullah, though both sides have denied any involvement in fraud or intimidation.

Steven Staples, the president of the Ottawa-based Rideau Institute think-tank, questioned how legitimate the election could be considered given the fraud allegations and the ongoing insecurity in the country.

"Perhaps it was just maybe a far overreach to think that a free and fair election can actually be held in the situation that Afghanistan is in," he said from Ottawa during an interview with CTV News Channel.

With files from The Associated Press