Two clear front-runners emerged in Afghanistan's presidential election Sunday as partial results showed a tight race between President Hamid Karzai's closest rival in the last vote and a former World Bank official.

With 10 per cent of the ballots counted, Abdullah Abdullah, who came in second in the disputed 2009 election, had 41.9 per cent, followed by Ashraf Ghani Ahmadzai with 37.6 per cent. In third place with 9.8 per cent of the vote was Zalmai Rassoul, another former foreign minister who was considered a favourite of Karzai.

Karzai himself was constitutionally barred from seeking a third term.

Officials cautioned the vote count could change as full preliminary results were not due until April 24, but the early numbers suggest none of the eight candidates was likely to get the outright majority needed to avoid a runoff.

Shortly after the results were announced, Abdullah told The Associated Press he has held talks with Rassoul but it was premature to discuss a possible alliance. He said he will seek a unity government if elected, but he appeared to rule out the possibility of including Ghani.

"Dr. Ghani could serve as a loyal opposition. That's also a service to the nation," he said in an interview at his house in Kabul.

Full results in mid-May

The chairman of the Independent Election Commission, Ahmad Yousuf Nouristani, said it was too soon to predict the outcome with so few of the more than 7 million ballots cast counted.

"Maybe today one candidate looks strong. Tomorrow, maybe another will pull ahead," he said.

Final results are to be declared in mid-May once complaints of fraud are fully investigated.

The man who replaces Karzai, the only president Afghans have known since the U.S.-led invasion ousted the Taliban in 2001, faces a huge task in fighting the insurgents and overseeing the withdrawal of the last foreign combat troops by the end of this year.

'These elections and their results are not legitimate. The country is occupied and there is fighting in the big cities. The winner and the loser are both criminals.' - Taliban spokesman Qari Yousef Ahmadi

The new president is also likely to sign a security agreement with the United States that would allow thousands of foreign troops to remain in the country to continue training security forces after 2014. Karzai — perhaps trying to shake off his image as a creation of the Americans — has refused to sign it, further chilling relations with Washington.

The election was held amid threats of violence by insurgents, who launched dozens of attacks in the run-up to the polls but largely failed to tamp down turnout.Abdullah, who has said he would sign the security pact within a month of taking office, told the AP his position has not changed.

The Taliban rejected Sunday's partial results.

"These elections and their results are not legitimate. The country is occupied and there is fighting in the big cities. The winner and the loser are both criminals," Taliban spokesman Qari Yousef Ahmadi said.

The results released Sunday are for 10 per cent of the vote in 26 of Afghanistan's 34 provinces. They represent a little over 500,000 ballots, Nouristani said.

Afghanistan Elections

Mohammed Nadir Mohseni, the spokesman of the complaints committee of the Independent Elections Commission, said 870 complaints filed are serious enough to potentially affect results. (Rahmat Gul/Associated Press)

Abdullah, who came in second to Karzai in the disputed 2009 election, had 212,312 votes. Ghani had 190,561 and Rassoul trailed with 49,821 votes. Numbers for the other five candidates were not announced.

Nearly 1,900 complaints of fraud have been filed, but the number is lower than that of the last election, said Mohammed Nadir Mohseni, the spokesman of the complaints committee of the Independent Elections Commission. Each allegation will be scrutinized so that there would be no question of the outcome of the April 5 vote, he said.

Of the complaints under investigation, 870 are serious enough to potentially affect results, he said. It was unclear if the majority of the alleged fraud favoured one candidate or another.

Widespread allegations of fraud marred the 2009 vote and led to a third of the ballots for Karzai being disqualified, depriving him of the majority needed to avoid a runoff. His nearest rival, Abdullah, quit before a second round could be held, saying he did not believe it would be fair either.

With files from Reuters