BASTION AIRFIELD, Afghanistan (Reuters) - An Afghan man driving a stolen pickup truck sped onto a runway ramp at an air base in southern Afghanistan and then emerged from the vehicle ablaze at around the time U.S. Defense Secretary Leon Panetta was arriving aboard a military plane, U.S. officials said.
The Pentagon chief, making an unannounced visit at a time of high tensions after a U.S. soldier massacred 16 Afghan villagers on Sunday, was not hurt in the incident at Bastion Airfield, a British base, and continued on with his schedule of events.
The Afghan man, a civilian who was not believed to be carrying explosives, was being treated at the base for severe burn injuries, U.S. officials said. No explanation was given for how the man caught on fire.
The pickup trunk apparently approached the runway ramp - where aircraft park - at high speed before ending up in a ditch, officials said.
U.S. officials did not rule out the possibility that the incident in southern Helmand province was an attempted attack on Panetta, but said there was no indication that this was the case. They said an investigation was ongoing.
"There is no evidence right now that the driver had any idea who was on that aircraft," U.S. Navy Captain John Kirby, a Pentagon spokesman, told reporters in Washington.
The incident was a reminder of the tense security situation in Afghanistan more than a decade after U.S. forces invaded to topple the Taliban rulers who had harbored the al Qaeda network responsible for the September 11, 2001, attacks on the United States.
Many questions about the incident remained after briefings by U.S. officials.
The Afghan man's vehicle neither caught fire nor exploded, and there were not explosives there either - raising questions about how he came to be on fire, Pentagon spokesman George Little said in Afghanistan, denying Afghan media reports.
"For reasons that are totally unknown to us at this time, our personnel discovered that he was ablaze," Little said.
"Base personnel put the fire out and he was immediately treated for burn injuries and is still being treated. He sustained considerable burn wounds," Little added.
One NATO service member was injured in the apparent car-jacking, U.S. officials said. This service member's nationality was not disclosed.
"A coalition member was injured in the theft of the vehicle," Kirby said. "... My understanding was (that the service member was) pulled out and potentially hit by the vehicle, too."
Tensions are high in Afghanistan in the wake of Sunday's massacre and the furor over the burning of copies of the Muslim holy book, the Koran, at a NATO base last month.
Reporters traveling with Panetta on his aircraft were not told about the incident for about 10 hours after it took place shortly before 11 a.m. local time. Panetta carried on with his schedule, talking to troops at Camp Leatherneck about the importance of the decade-old war effort.
Shortly before he arrived to speak, U.S. troops and other allies were told to put their weapons outside the tent - a highly unusual move that officials downplayed later. The commander in Helmand, U.S. Major General Mark Gurganus, said he wanted foreign troops to be unarmed since Afghan troops would be.
Little said the removal of the firearms and the incident involving the pickup truck were "absolutely not" linked.
Panetta's team apparently became aware that something was amiss shortly before landing at Bastion but details only came later.
"We did know that we were diverted to a different runway. And we learned soon after landing that there may have been an incident," said Little, who was traveling with Panetta.
"Again, the security of the secretary was never in question. He carried on during the event."
Additional reporting by David Alexander and Missy Ryan in Washington; Editing By Warren Strobel and Will Dunham