Kabul ? Citing “clear and convincing evidence of fraud,” an Afghan election complaints commission on Tuesday ordered an audit and a recount of votes at numerous polling sites across this warring nation.

The order came on a pivotal day in the drawn-out — and increasingly tense — aftermath of the Aug. 20 presidential election.

In the afternoon, President Hamid Karzai was tentatively awarded enough votes to claim a second term as president. The new voting tallies give him more than 54 percent of the vote, well over the 50 percent threshold required to avoid a run-off with his major challenger, Abdullah Abdullah.

The post-election drama unfolds as the Karzai government’s power in Afghanistan erodes amid insurgent gains in northern and other provinces that once were stable. On Tuesday, in Kunar province, insurgents set an ambush, killing four U.S. Marines, eight Afghan troops and police officers, and an interpreter. Also on Tuesday, in the capital city of Kabul, a suicide bomber drove his car into a convoy that was approaching the military gate of the airport, killing at least three Afghan civilians and wounding six.

The suspected wide-scale fraud cited by the Electoral Complaints Commission, a United Nations-backed body, could be a major setback for the Obama administration’s hopes that the elections would strengthen Afghanistan’s weak central government. The United States and its allies sent thousands of additional troops to provide security for the polling.

In Washington, Obama spokesmen acknowledged that there clearly were electoral improprieties, but expressed hope that the election will be seen as fair if the complaints are adjudicated.

“These elections need to be credible and need to reflect the will of the Afghan people,” State Department spokesman Ian Kelly said. “And a legitimate electoral process is vital to us … and vital to any kind of partnership that we would have with the (Afghan) government going forward.”

“It’s better to get this all out,” said a senior State Department official, who spoke only on the condition of anonymity in order to talk more openly, referring to the airing of the fraud allegations. “The real problem is, how do we get to a result that everybody’s got confidence in?”

The progress of the vote count has been closely monitored by NATO countries that have sent soldiers, civilians and aid money to Afghanistan in a bid to help stabilize the nation and prevent the Taliban from returning to power. They’ve become disillusioned with Karzai’s government and have helped press the case for a major investigation of election fraud.

It will take weeks, or even months, for final election results to be decided.

Karzai’s victory could yet be derailed if the investigation strips away enough votes. A Karzai adviser appeared confident Tuesday that that won’t happen.

“We’re not actually declaring officially, but we think we are the winner,” said Moen Marastyal, an adviser to the Karzai campaign.