KABUL, Afghanistan — A suicide car bomber attacked an American military convoy on the road to Kabul's airport on Saturday, killing a U.S. soldier and a four Afghan civilians, officials said.

The bombing — on the sixth anniversary of the U.S.-led invasion of Afghanistan — threw several vehicles on their side. Four Afghans were killed and 12 others wounded, the Health Ministry said.

The attack was against U.S. troops responsible for training the Afghan military and police. Lt. Col. David Johnson, a U.S. spokesman, said one American soldier died in the blast and one was wounded.

Dozens of shops were damaged.

"There was an enormous explosion, the windows of my shop shattered," said tailor Mohammad Isaq. "When I came out I saw the foreigners' vehicles on fire. I saw two injured Afghans and I ran to help them."

This year has been the most violent of the six-year effort, the result of the U.S.-led invasion to oust the Taliban for hosting al-Qaida leader Osama bin Laden following the Sept. 11 terrorist attacks on the U.S.

More than 5,100 people have died in insurgency-related violence in 2007, according to an Associated Press count based on Afghan and Western officials.

The suicide bombing was the third major attack in Kabul in a week. On Sept. 29, a bomber targeted an Afghan army bus, killing 30 people. A similar attack Tuesday against a police bus killed 13.

BAGHDAD — U.S. airstrikes killed at least 25 people Friday after troops met a fierce barrage while hunting suspected arms smuggling links between Iran and Shiite militiamen. The military described the dead as fighters, but village leaders said the victims included children and men protecting their homes.In a separate incident, the U.S. military said it was investigating the deaths of three civilians shot by American sentries near an Iraqi-manned checkpoint. Iraqi officials said the victims were U.S.-allied guards and were mistakenly targeted.While details could not be independently confirmed, both reports reflected rising concerns about possible friendly fire killings as more viligante-style groups join the fight against extremists and fill the vacuum left by Iraq's collapsing national police force.Such claims could hinder crucial U.S. efforts to draw Sunni and Shiite leaders into alliances against insurgent factions such as al-Qaida in Iraq. In a series of raids around Iraq, U.S. troops killed 12 suspected insurgents linked to al-Qaida, the military said.Meanwhile, four American soldiers were reported killed — three Friday in roadside bombings in Baghdad and near Beiji to the north, and one Thursday in a small-arms attack in the capital.At least 3,813 members of the U.S. military have died since the Iraq war started in March 2003, according to an Associated Press count.