KABUL - Afghanistan's U.N.-appointed election watchdog said on Tuesday it had found clear and convincing evidence of fraud in last month's presidential election and ordered a recount of suspicious returns.

The announcement came on the same day a suicide car bomber blew up his vehicle outside a NATO military base at Kabul's main airport killing three civilians, the Afghan capital's worst attack since the vote.

The Electoral Complaints Commission (ECC) said returns must be recounted and audited for any polling station where more than 600 votes were recorded -- the most authorities believe should have been cast at any station -- or where any candidate received more than 95 percent of the vote if more than 100 were cast.

International officials initially hailed the August 20 election because Taliban fighters failed to scupper it. As fraud charges mount, however, those assessments have become more guarded.

Recent tallies have shown President Hamid Karzai just shy of the 50 percent majority needed to win in a single round without a run-off, with uncounted votes from the heartland of his support in the south appearing likely to put him over the top.

His main challenger, Abdullah Abdullah, says many of those southern votes are fake, a charge given stronger credibility by the ECC's findings.

In the course of its investigations, the ECC has found clear and convincing evidence of fraud in a number of polling stations, the body said in a statement.

Most of the stations where it found fraud had either a larger than expected number of total votes cast, or a higher than expected proportion cast for a single candidate, it said.

The ECC is led by a Canadian and three of its five members were appointed by the United Nations. It has the power to set aside results as reported by Afghanistan's own Independent Election Commission. The IEC was due to release nearly-complete preliminary results later on Tuesday.

ATTACK SHOWS DETERIORATING SECURITY

The airport attack was a further demonstration of deteriorating security at a time violence is at its worst, the unresolved election has put the country's political future in doubt and Western popular support for the war is rapidly eroding.

The head of criminal investigations for Kabul police, Abdul Ghafar Sayedzada, said three civilians were killed and six wounded in the airport attack. No foreign troops were killed, though four were lightly injured, NATO said.

Huge flames could be seen rising from the blast site and the wail of sirens could be heard several kilometers from the civil-military airport, which has experienced a series of Taliban rocket attacks and a suicide strike in the past.

A Taliban spokesman said by phone from an undisclosed location the militants were responsible for the blast, targeting Western forces. The attack came less than a month after a suicide car bomber struck the NATO headquarters entrance in Kabul, killing at least seven people and wounding 100.

Increased violence in Afghanistan has sapped public support for the war in the United States, which now has about 65,000 troops among the 103,000 foreign troops there.

GERMAN LEADER UNDER FIRE
The war has also become a matter of major controversy in Germany three weeks before a general election, after German troops called in a U.S. air strike last week that Afghan officials say killed scores of people, many of them civilians.

Karzai called the decision to bomb hijacked fuel trucks in the north of Afghanistan a major error of judgment.

The NATO-led International Security Assistance Force (ISAF) announced the start of a formal investigation into the incident, led by a Canadian general. For the first time, the force said clearly on Tuesday it believed civilians had been killed.

Subsequent review has led ISAF to believe that along with insurgents, civilians also were killed and injured in the strike, it said in a statement.

Chancellor Angela Merkel, defending her government's Afghanistan policy in parliament on Tuesday, rejected premature criticism of the air strike -- the deadliest incident involving German troops since World War Two --and promised a full account.

She and British Prime Minister Gordon Brown, another European leader facing a backlash at home over support for the war, have called for a conference this year to set a timetable to hand over responsibility for Afghan security to Afghans.

Any such decision is far more likely to be in the hands of U.S. President Barack Obama, who has made the Afghan war a priority of his administration but now must decide whether to send yet more troops. Together, Britain and Germany account for just 13 percent of the NATO-led force.

The incident last Friday is also a test for NATO commander General Stanley McChrystal, who took charge of the force three months ago vowing to protect Afghan civilians. He has gone on television to reassure Afghans he is investigating the strike.

(Additional Reporting by Sayed Salahuddin, Hamid Shalizi and Jonathon Burch; Writing by Peter Graff; Editing by Jerry Norton)

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