(Adds U.S. soldiers wounded, details)

KABUL, March 13 (Reuters) - A suicide car bomber killed six Afghan civilians in an attack on U.S. troops near the airport in Afghanistan's capital on Thursday, officials said.

Four of the soldiers received minor injuries and 13 more civilians were also wounded in the attack, which came near a roundabout close to Kabul international airport during the morning rush-hour.

"Six civilians have been killed in the attack and the bomber used a car," Deputy Interior Minister Munir Mangal told Reuters near the scene.

A bomber in a black car struck the convoy, wounding four soldiers and heavily damaging one vehicle, said a spokesman for the NATO-led International Security Assistance Force (ISAF).

The soldiers were not members of the 42,000-strong ISAF force, but part of a smaller unit which trains the Afghan army and police, a spokesman for that force said.

The four U.S. soldiers received only minor cuts and bruises, he said.

The Taliban claimed responsibility.

"The foreign occupying forces and their Afghan slaves should get ready for the mujahideen's suicide and guerrilla attacks this summer. This new year will be bloodiest," spokesman Zabihullah Mujahid said by telephone from an unknown location.

The Taliban have threatened to target the capital Kabul with more suicide bombings this year in their campaign to topple the pro-Western Afghan government and eject foreign troops.

The hardline Islamist movement carried out around 140 suicide bombings across the country in 2007, but foreign forces have become better at avoiding casualties and most of those killed, some 200 last year, were civilians. (Reporting by Kabul newsroom and Saeed Ali Achakzai in Spin Boldak; Writing by Sayed Salahuddin; Editing by Jerry Norton)

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