KABUL - President Hamid Karzai defended Afghanistan's disputed presidential election on Thursday after early results showed him the winner, while a suicide bomb attack on Italian troops tested the resolve of a major NATO ally.

Sixteen people, including six Italian soldiers, died in the attack on an Italian military convoy within walking distance of the presidential palace, minutes after Karzai held a news conference there.

It was his first such encounter with reporters since the Aug 20 election and he praised Afghans for braving violence to vote.

The strike, the deadliest on Italian forces in Afghanistan, caused shock back home as European leaders scramble to bolster flagging support for the eight-year-old war.

The disputed election has further eroded public backing among NATO allies for the war effort, at a time when U.S. President Barack Obama is considering whether to send more troops and European allies are debating whether to quit.

Complete preliminary results released on Wednesday showed Karzai winning the election in a single round with 54.6 percent of the vote, enough to avoid a run-off against his main challenger, former foreign minister Abdullah Abdullah.

But the outcome may not be final for weeks or months, held up by lengthy investigations of ballot stuffing. A U.N.-backed watchdog has ordered a recount of 10 percent of polling stations, saying it found clear and convincing evidence of fraud.

Karzai played down suggestions fraud could have been big enough to overturn the outcome and force a second round run-off.

Like other elections of the world ... there were problems and sensitivities in the Afghanistan elections, but it has not been to the extent which the media speak of, he said.

I believe firmly, firmly in the integrity of the election and the integrity of the Afghan people, and the integrity of the government in that process.

Western officials initially hailed the August vote, mainly because militant attacks failed to prevent it from taking place. Their response has since become more equivocal.

An EU observer mission has said more than a third of Karzai's votes might be suspect because of fraud. Karzai's campaign has called those claims irresponsible.

Abdullah says fraud played a decisive role and needs to be removed in the complaints process for the result to be valid.

The extent of fraud was massive. ... A golden opportunity for Afghanistan has turned into a disastrous situation, Abdullah told reporters, adding he was not interested in Karzai's repeated offers of a government post.

My position is not to get a post from the government but to bring change. That will remain my agenda. I am not interested in a coalition government.

The Taliban claimed responsibility for the suicide strike in a text message sent from a phone number used by a Taliban spokesman.

At the scene, Afghan troops ferried wounded civilians to ambulances near several wrecked Italian military vehicles.

The body of at least one dead Italian soldier lay in the street in front of an armored truck that bore an Italian flag. Other body parts were scattered near the scene. The chassis of an exploded car had landed dozens of meters away.

Record military and civilian deaths as well as uncertainty over the election result have raised questions among Washington's allies, particularly Britain and Germany, about how long their troops should remain or whether they should be there at all.

Italy's parliament held a minute's silence in honor of the victims, but political debate over the mission quickly resumed.

Most of the conservative government and the main center-left opposition broadly support the Afghan mission. Interior Minister Roberto Maroni said pulling out Italian troops would mean surrendering to the logic of terrorism.

The far left restated demands for an immediate withdrawal.

The Italian military contingent's presence in Afghanistan is the fruit of a mistaken policy and strategy. Italian troops should be withdrawn immediately, said communist leader Paolo Ferrero.

Obama may also find it difficult to persuade Americans to send more troops to defend a government whose legitimacy could be called into question due to large scale fraud, diplomats say.

Addressing reporters on Thursday, U.S. Vice President Joe Biden said it was too early to talk about additional troops.

We don't have all the resources that were authorized in place yet. Most of the military is just getting there, he said. It is very premature in my judgment to make any decision about additional resources.

(Additional reporting by Golnar Motevalli and Peter Graff, by Francesco Guarascio in BRUSSELS, Stephen Brown in ROME; Writing by Peter Graff and Maria Golovnina; Editing by Ron Popeski)