KANDAHAR, Afghanistan - A Taliban suicide car bomber killed an American soldier and two Afghan civilians Thursday near a U.S. military base shortly after the visiting U.S. defense secretary left the facility in southern Afghanistan, officials said.

The attacker targeted a moving vehicle near the access gate to the military side of Kandahar's airport, according to an Afghan Defense Ministry spokesman, Gen. Mohammad Zahir Azimi.

It was unclear whether the blast had anything to do with U.S. Defense Secretary Leon Panetta's unannounced visit to Kandahar Air Field earlier Thursday. The sprawling facility houses more than 20,000 service members from 20 countries and has more than 11,000 civilian contract workers.

Panetta said one American soldier was killed and three others wounded. Azimi said two Afghan civilians were killed and 14 wounded.

Taliban spokesman Qari Yousef Ahmadi claimed responsibility for the attack in an e-mail, saying a suicide car bomber had targeted foreign military vehicles stopped near the gate of Kandahar Air Field.

Panetta was at the air field for about three hours, receiving a briefing from U.S. Army Maj. Gen. Robert Abrams, the region's top coalition commander. Panetta also spoke to about 350 U.S. troops and took questions from them before flying back to Kabul.

Panetta's press secretary, George Little, confirmed the suicide car bombing occurred, adding that coalition officials were assessing the situation.

A U.S. official said early indications were that the attacker did not breach the base's perimeter. The official spoke on condition of anonymity because the matter was in the early stages of investigation.