KABUL: Afghan President Hamid Karzai's controversial alliances with warlords came under fire Sunday during his first live television debate with his leading challengers at crunch polls this week.

Outspoken anti-corruption campaigner Ramazan Bashardost and former finance minister Ashraf Ghani criticised the head of state in a 90-minute head-to-head -- the first time a sitting Afghan president has attended such an event.

The alleged deals, which could see Karzai win the August 20 vote, have disillusioned Afghans and Western backers of the country's move towards democracy after the 2001 US-led invasion ousted the extremist Taliban regime.

"There are those who claim they are fighting warlords, but today warlords have the main role in their campaign, and (one) is their first vice president, this is not acceptable for the people of Afghanistan," charged Bashardost.

Karzai has picked Mohammed Qasim Fahim, accused of a range of abuses including during the 1990s civil war, as his first vice president and has also won over other ethnic and factional leaders who have substantial followings.

Anyone who "oppressed" people during past conflicts -- against the communist regime, during the civil war and under the 1996-2001 Taliban administration -- was "unacceptable," Bashardost said.

The incumbent has defended his allies, who include one of Afghanistan's most feared warlords Abdul Rashid Dostam, claiming it is in the interests of national unity.

Karzai adopts a "big tent" approach aimed at bringing together strongmen behind the ethnically fraught civil war that destroyed Kabul in the 1990s.

But Bashardost said national unity was not a matter of accepting "the worst of them," adding he was not prepared to say specifically who he was alluding to.

"If I mention names, there will be bottle fighting among us," he quipped, referring to occasions in parliament when argumentative lawmakers have hurled plastic bottles at each other.

The debate put Karzai in the rare position of facing some of his harshest critics and he came under fire for pulling out of an earlier debate in July.

Ghani, an academic, also took aim at Karzai's alliances. "I have not struck any deals with any warlord, have not given any ministry, governor's position, or a part of Afghanistan to any of them."

Ghani is running on a campaign of clean governance, job creation and economic development -- issues that he raised in a debate that also touched on efforts to defeat the Taliban insurgency and foreign troop deployments.

He and Bashardost are considered two of the main challengers to Karzai on voting day, when there will be 41 names on the ballot paper. However, the president's top rival Abdullah Abdullah was absent from the stage.

It was not immediately clear why he did not attend.

Karzai, who is expected to win but may not be able to avoid a run-off, hit back at the accusations of forging "coalitions" of convenience.

"If -- for the national interest, for progress, for national unity, avoiding war... there is need for more such convenience, once again I will seek that. A thousand times I will do that," he said.

He insisted he had the experience needed to push Afghanistan closer to peace and prosperity.

"Despite big achievements, our country still has serious and huge problems: peace has not become countrywide, there's no security in Afghanistan and our other wishes for development and prosperity have not come true," he said.

"I think with the experience I have, the patience I have, the tolerance I have and the vision I have, I can be of service for Afghanistan for another five years."

Thursday's election is a key juncture in Afghanistan's difficult transition to democracy -- a route chosen after the Taliban's removal in the US-led invasion aimed at the Al-Qaeda network behind the September 11 attacks.

However, there are fears that the threat of insurgent attacks could keep voters away from polls, undermining the credibility of the vote.