KABUL: Leading Afghan presidential candidate Ashraf Ghani Ahmadzai praised Hamid Karzai for allowing the country's first democratic transition of power and said Thursday that he'll offer the longtime leader an advisory role if he wins this weekend's election.

Ahmadzai spoke to The Associated Press in a wide-ranging interview two days before Afghans go to the polls to choose a new president.

Karzai has been Afghanistan's sole leader since the Taliban were ousted in 2001 and many feared he would try to extend his tenure. But he has vowed to step down as required by the constitution, which bars him from seeking a third term.

''President Karzai took office under extremely difficult circumstances and he's the first man in our 5,000 years of recorded history that is voluntarily ceding power under a constitution based on the will of the people to his successor,'' Ahmadzai said.

''If I'm that successor, I'll be honouring that president by seeking his advice and by creating a special office as the first elected president of the country where he would have a role and a voice in national affairs, regional affairs and international affairs."

The 64-year-old Ahmadzai is considered one of the main contenders in a crowded field of eight candidates. The other two front-runners are Abdullah Abdullah, who was Karzai's main rival in the disputed 2009 election, and former Foreign Minister Zalmai Rassoul.

Most experts doubt any of the candidates will get the majority needed for an outright win in Saturday's vote so a runoff is widely anticipated.

Ahmadzai also said he supports peace talks aimed at bringing the Taliban into the political process, but stressed the best way to force the militant movement to give up violence is to improve governance and chip away at their public support.

''The power of veto through violence is unacceptable,'' he said. ''Once we mobilise the Afghan public for a genuine true peace — for which we are willing to pay the price — then I think the Taliban will either join the political process or will be isolated because it's not the government that can isolate them, it's the public that can make the decisive move.''

The Taliban have vowed to disrupt Saturday's vote and have staged a series of high-profile assaults in the Afghan capital that have raised fears they will follow through on warnings to target election workers and polling centres. A suicide bomber struck an entrance gate of the heavily fortified Interior Ministry on Wednesday, killing six policemen.

Ahmadzai is a former finance minister and World Bank official and a well-known academic. He also ran for president in 2009 but received just three per cent of the vote. Later, he chaired a commission in charge of transitioning responsibility for security from the US-led coalition to Afghan forces.

He said that if elected, he will sign a security agreement with the United States, defending the pact as the best way to professionalise Afghan security forces and establish the country's sovereignty.

Karzai surprised the international community and many Afghans when he refused to sign the deal despite a recommendation to do so by a gathering of Afghan tribal elders and other dignitaries in December.

The US and its Nato allies are due to withdraw their combat forces by the end of this year, and the bilateral security agreement would allow thousands of foreign troops to remain to help train and mentor Afghan security forces. Billions of dollars in aid money also are at stake.

''I will be submitting the bilateral security agreement to parliament within the first week and as soon as parliament approves, it I'll be signing it,'' Ahmadzai said.

''The country needs confidence, our security forces need confidence. The economy is deteriorating and at a standstill because of lack of confidence over this agreement.''

Ahmadzai, who studied in the US but returned to Afghanistan after the Taliban were ousted, said he doesn't believe that a runoff is a foregone conclusion.

He expressed confidence that his aggressive campaigning in recent weeks during which he shuttled between provinces for mass rallies and participated in public debates has given him a strong advantage.

Ahmadzai also pointed out that he was the only candidate to appear at one televised debate focusing on the economy earlier this week.

''The number of people who are undecided, I think are making up their minds, and all the signs point out that what we have presented to the public...has made a decisive shift,'' he said, sitting in a reception room that was modelled after a mosque with nine domes.

''With this in mind I think victory in the first round is possible.''