Afghan presidential candidate Ashraf Ghani pledged on Sunday to fight on after coming second in preliminary election results, setting the stage for a difficult run-off vote likely to be targeted by Taliban militants.

Another expensive, and potentially violent, election could be avoided by negotiations between the two leading candidates in the coming weeks, but both men have dismissed talks of a possible power-sharing deal.

Ghani, a ex-World Bank economist, secured 31.5 per cent of the vote, behind former foreign minister Abdullah Abdullah on 44.9 per cent, in the election on April 5 that began Afghanistan’s first democratic transfer of power.

“In the second round, the people should decide who has the ability to bring changes to the system,” Ghani told supporters in Kabul. “We will go for a second round with determination. Our belief in victory is still strong.”

As no candidate gained more than 50 per cent, a run-off between the two leading names is required under the Afghan constitution. Ghani said that investigations into fraud could change the percentages before final results are due on May 14.

“After inspection of fraud, the distance between the two top candidates will lesson,” he said.

“A second round is a must according to constitution. Any doubts will threaten the stability of Afghanistan”.

“We will go for principles not deals,” he added.

“The people’s votes tell me not to strike any deals with anyone behind the curtains”.

“We are ready, the people are ready, I call on the international community not to doubt our determination.”

The head-to-head election due on June 7 will choose a successor to President Hamid Karzai, who has ruled since the Islamist Taliban regime was ousted in 2001 and who is constitutionally barred from serving a third term.

Whoever wins will have to oversee the fight against a resilient Taliban insurgency as 51,000 US-led troops depart this year, as well as strengthen an economy that relies on declining aid money.

Eight men ran in the election, with polling day hailed a success by Afghan officials and foreign allies as the Taliban failed to launch a major attack despite threats to disrupt the vote.

The 2009 election, when Karzai retained power, was marred by fraud in a chaotic process that shook confidence in the multinational effort to develop the country and also marked a sharp decline in relations with the United States.

The United Nations’ mission in Afghanistan welcomed today’s results, but warned election officials that they must address all complaints “in a professional, expeditious and open manner” to safeguard the election process.