A powerful bomb exploded Friday near a U.S. military convoy, wounding at least one American soldier and raining debris over a wide area, the U.S. military said. Afghan officials said four U.S. soldiers were injured.

A purported Taliban (search) spokesman claimed responsibility for the attack, one of several reported across southern Afghanistan late Thursday and Friday. More than 600 people — including soldiers, international workers and civilians — have died in violence in Afghanistan this year.

In a statement, the U.S. military said the blast was caused by a roadside bomb. The soldier, whose name was not released, was in stable condition and awaiting evacuation to Landstuhl Regional Medical Center (search) in Germany. The vehicle he was traveling in was damaged.

Afghan police and government officials put the casualty toll higher and said the bomb appeared to be hidden in a taxi on the side of the road.

"When our forces reached the scene of the explosion, they saw four American soldiers lying on the road covered in blood. They were seriously wounded," said Gen. Salim Khan, deputy police chief of Kandahar province (search).

Khalid Pashtun, a spokesman for Kandahar's governor, also said four soldiers were injured, as did another policeman at the scene, Tor Jan, and several Afghan witnesses. It was impossible to immediately clarify the discrepancy between their account and that of the U.S. military.

A purported Taliban spokesman, Abdul Hakim Latifi, claimed responsibility for the bombing.

"We carried out the attack on the U.S. forces," he said in a satellite phone call to The Associated Press from an undisclosed location. "We have said it again and again that we will fight jihad against U.S. forces, their international allies and their Afghan supporters."

Latifi has contacted AP and other news organizations with Taliban statements in the past, and appears to speak for the group. However, it is impossible to independently verify his comments.

About 60 U.S. solders and more than 100 Afghan security forces cordoned off the area, a busy road leading from the American base to the center of town, warning journalists not to take pictures. But the charred remains of one car — presumably the one carrying the bomb — could be seen. It appeared to be a taxi.

Khan said authorities believed the bomb was set off by remote control, as no body was found inside the wreckage.

U.S. soldiers, with bomb-detecting dogs, were frisking at least six men made to sit on the ground with their hands raised in the air.

Kandahar is the main city in southern Afghanistan and home to a large U.S. base. It has been the site of frequent attacks, usually against convoys making their way on dusty roads.

Meanwhile, suspected Taliban rebels shot at Afghan government troops and election workers in two separate attacks in Helmand province, which borders Kandahar to the west. The attacks sparked shootouts in which four fighters were killed, said Haji Mohammed Wali, spokesman for the Helmand governor.

The first attack occurred late Thursday in the Mama Karez district as the soldiers patrolled in a pickup truck. Three Taliban soldiers were killed during the one-hour shootout that ensued. Later Thursday, two Taliban militiamen riding on motorcycles opened fire on two pickup trucks carrying Afghan election workers in Lashkargah, the capital of Helmand, Wali said.

Security guards accompanying the election officials returned fire, killing one attacker, he said. The election workers were not hurt.

The bombing in Kandahar comes one day after the military announced the pullout of the 2,400-strong 22nd Marine Expeditionary Unit patrolling southern Afghanistan since March. The Marines were staying at the Kandahar base awaiting their departure to American warships in the region.

The Camp Lejeune, N.C.-based force had killed more than 100 enemy fighters during their tour of duty, losing just one of their own.

They were part of a push to beef up the U.S. presence here ahead of landmark October elections, but their pullout was widely expected because of the normal rotation of Marine Expeditionary Units.

Taliban remnants and Al Qaeda fighters have managed to keep up a drumbeat of violence, much of it against election workers, leading to concern whether the vote will be able to take place in a free and fair atmosphere.