A U.S. service member and two civilians were killed Thursday in a suicide bombing in the southern city of Kandahar that coincided with a surprise visit to the country by U.S. Secretary of Defense Leon Panetta, an Afghan official told Efe.

The blast occurred at 5:00 p.m. at the entrance to Kandahar Airfield and was aimed at a convoy of personnel from the NATO-led International Security Assistance Force, provincial government spokesman Javed Faisal said.

The attacker rammed an explosives-packed vehicle into the convoy, Faisal said.

Besides the three fatalities, the attack left 18 civilians wounded.

Speaking on condition of anonymity, another Afghan official told Efe the bombing took place "hours" Panetta left Kandahar on a plane bound for Kabul.

The Pentagon chief arrived in the country Wednesday on an unannounced visit his aides said is aimed at gathering information as Washington considers the nature of the continuing U.S. presence in Afghanistan after the withdrawal of NATO forces, set for the end of 2014.

Panetta's previous visit to Afghanistan, in March, was also marked by an attack on a NATO base.

Conflict continues to rage in Afghanistan more than a decade after the U.S. invasion and the fall of the Taliban. EFE