An apparent suicide bomber detonated explosives in his car Monday near a U.S. military vehicle in southern Afghanistan, wounding four Americans in the latest assault on coalition forces, a U.S. military spokesman said.

The four injured soldiers, one of them in serious condition, were evacuated by air to a U.S. base in Kandahar for medical treatment, said Lt. Col. Jerry O'Hara.

Gen. Salim Khan, the deputy police chief for Kandahar, said the attack occurred on a highway near the city. The head of the attacker was found near the site of the blast and it appeared to be that of an Arab, he said.

Khan said at least three American soldiers were killed, but the U.S. military said none had died. An Associated Press reporter saw three American soldiers being carried on stretchers into a military helicopter.

Mullah Latif Hakimi, who identifies himself as a Taliban spokesman, said in a telephone call to the Associated Press that the group was responsible for Monday's bombing and that the suicide attacker was an Afghan.

The bombing followed a recent surge in attacks by Taliban-led rebels. A bomb attack Sunday on an Afghan family's pickup truck north of Kandahar killed one woman and wounded four others. On June 1, a suicide bomber killed 20 people at the funeral of an anti-Taliban cleric in Kandahar.