By AMIR SHAH and HEIDI VOGT, Associated Press Writers
KABUL – A suicide bomber killed three American troops and three Afghan civilians after ramming an explosive-laden vehicle into a military convoy in eastern Afghanistan on Tuesday.

The convoy was rocked by the blast outside the capital of Kapisa province north of Kabul, said Lt. Commander Christopher Hall, a spokesman for NATO forces.

Three U.S. troops were killed in the explosion, said Tech. Sgt. Chuck Marsh, a U.S. military spokesman. The soldiers served with NATO's International Security Assistance Force.

Three civilians also died and two others were wounded after the Toyota Corolla smashed into the convoy, the Interior Ministry said in a statement.

"I was driving my motorbike when I saw the car with a young man with a beard and white cap," said Sayed Najibullah, a 22-year-old shopkeeper.

Najibullah said the driver waved him past the car and the convoy, and he heard a large explosion behind him a few minutes later.

Taliban regularly use suicide attackers and roadside bombs in assaults on foreign and Afghan troops across the country. Such attacks were up 25 percent the first four months of 2009 compared with the same period last year.

Bomb attacks will rise 50 percent this year to 5,700 — up from 3,800 last year, U.S. military officials predict.

According to military figures, 172 coalition forces were killed in such attacks last year — and far more Afghan civilians died.

Meanwhile, in the eastern border province of Khost, a convoy of Afghan and American troops killed the driver of a car when the vehicle did not slow down in response to shouts to stop and warning shots, said Chief Petty Officer Brian Naranjo, a U.S. forces spokesman.

"They fired to stop the vehicle and killed the driver," Naranjo said.

In the south, U.S. forces said they killed eight Taliban fighters in a clash Uruzgan province on Monday. The coalition said two of its troops and three Afghan policemen were wounded during the clash.

They were undergoing medical treatment and were in stable condition. The troops were on patrol when Taliban fighters attacked with small-arms fire and heavy machine-guns.

Southern Afghanistan is the center of the Taliban-led insurgency, where thousands of new American troops will join the fight this year.

President Barack Obama hopes the new troops can turn the tide of the Taliban successes in the last three years.