(CNN) - A suicide bomber exploded a car bomb Thursday near Afghanistan's Kandahar airfield hours after U.S. Defense Secretary Leon Panetta had left the southern Afghan city.

Panetta's delegation was never in danger, said a U.S. official traveling with him, who confirmed details of the blast.

The bomb, which exploded at about 5 p.m. local time, targeted "a foreign forces convoy," Jawid Faisal, a spokesman for the governor of southern Kandahar province.

One International Security Assistance Force service member and two Afghan civilians were killed, and three ISAF service members and 18 Afghan civilians were injured, he said.

Coalition spokesman Lt. Col. Hagen Messer confirmed the bombing, saying the ISAF investigation team was at the scene.

"I don't know at this point if this was in any way linked to our visit," said the U.S. official traveling with Panetta.

Pentagon press secretary George Little confirmed the explosion was a vehicle-borne improvised explosive device.