Leon Panetta
© Pool photo/Scott OlsonDefense Secretary Leon E. Panetta arrived at Forward Operating Base Shukvani, Afghanistan, on Wednesday.
Kabul, Afghanistan - A tense visit to Afghanistan by Defense Secretary Leon E. Panetta got off to an alarming start on Wednesday when a stolen pickup truck sped onto a ramp alongside a runway at a British military airfield and crashed into a ditch as Mr. Panetta's plane was landing.

Mr. Panetta was not hurt, but Pentagon officials said the Afghan driver emerged from the vehicle in flames.

No explosives were found on the driver, a civilian, or in the truck, the officials said, and the Pentagon was not immediately considering the episode an attack on Mr. Panetta. But it reinforced the lack of security in Afghanistan at the beginning of his two-day visit, the first by a senior member of the Obama administration since an American soldier reportedly killed 16 Afghan civilians, mostly children and women, in Kandahar Province. The visit had been planned months ago, but took on new urgency after the Sunday massacre.

Mr. Panetta, like President Obama, has denounced the deaths and vowed to bring the killer to justice, a message he was to deliver in person to President Hamid Karzai of Afghanistan. The killings have further clouded already strained Afghan-American relations. On Thursday morning, an American official said the suspect had been moved out of Afghanistan to Kuwait. That is likely to further anger Afghans, who called for him to be tried in their country.

The truck crashed as Mr. Panetta landed at Camp Bastion, a British airfield next to Camp Leatherneck, a vast United States Marine base in Helmand Province.

Mr. Panetta and his aides were aware of the crash shortly after it happened, about 11 a.m., but he continued as planned, meeting with local Afghan officials; delivering remarks to 200 Marines, other international troops and Afghan security forces at Camp Leatherneck and then heading to a remote combat outpost, Shukvani, in western Helmand.

Mr. Panetta's aides did not disclose the crash until nearly 10 hours later, well after Mr. Panetta had arrived in Kabul from his day in the south, and at least an hour after the British news media began reporting it. It was not clear if the aides would have made the disclosure had word not leaked out.

Defense officials said Mr. Panetta's plane had been diverted away from the truck, which ended up in the ditch off the ramp, an area where Mr. Panetta's plane had been expected to park. The Pentagon press secretary, George Little, said he did not know whether the truck reached the ramp parking area "while we were landing or before or slightly after."

Mr. Little said that the stolen vehicle had not exploded, contrary to some earlier reports, and that Mr. Panetta had never been in danger. But he could not explain the Afghan's motive or explain why he was on fire. "For reasons that are totally unknown to us at this time, our personnel discovered that he was ablaze," Mr. Little said. "He ran, he jumped on to a truck, base personnel put the fire out, and he was immediately treated for burn injuries."

In Washington, Capt. John Kirby, the Pentagon spokesman, said the truck had been stolen from a coalition service member - he did not give a nationality - who was wounded in what was apparently a carjacking. There was no immediate evidence that the Afghan driver "had any idea who was on that aircraft," Captain Kirby said.

Mr. Panetta flew from Washington to Manas, Kyrgyzstan, on his usual plane, a reconfigured Boeing 747 with "United States of America" emblazoned on the side, but as usual for security reasons, he transferred to a gray C-17 military cargo plane for the unannounced trip to Afghanistan.

In a sign of the nervousness surrounding the trip, a sergeant major abruptly told the Marines gathered to hear Mr. Panetta in a tent at Camp Leatherneck to get up, place their M-16 and M-4 automatic rifles and 9-millimeter pistols outside, and return unarmed. The sergeant major, Brandon Hall, told reporters that he was acting on orders.

"All I know is I was told to get the weapons out," he said. Asked why, he replied: "Somebody got itchy - that's all I've got to say. Somebody got itchy. We just adjust."

Normally, American forces in Afghanistan keep their weapons when the defense secretary visits and speaks to them. The Afghans in the tent had not been armed to begin with, as is typical.

Later, American officials said that the top military official in Helmand, Maj. Gen. Mark Gurganus, had decided on Tuesday that no one would be armed while Mr. Panetta spoke, but that word had not reached those in charge in the tent until shortly before Mr. Panetta was due to arrive.

General Gurganus told reporters later that he had wanted a consistent policy for everyone in the tent, and that "I wanted to have the Marines look just like their Afghan partners," noting, "You've got one of the most important people in the world in the room." He insisted that his decision had had nothing to do with the massacre; later, defense officials said the decision had had nothing to do with the truck at the airfield.

In his remarks to the Marines, Mr. Panetta vowed to not allow the Kandahar killings to accelerate the American withdrawal from Afghanistan. "We will be challenged by our enemies. We will be challenged by ourselves. We will be challenged by the hell of war itself," he said.

Mr. Panetta then flew to Combat Outpost Shukvani, where Marines fight alongside troops from the former Soviet republic of Georgia. The commander of the 750 Georgian troops, Lt. Col. Alex Tugushi, lost both legs in an explosion from a homemade bomb in December; he is recovering at the National Naval Medical Center in Bethesda, Md., where President Obama has visited him.

Mr. Panetta read a letter to the Georgians from Colonel Tugushi that said in part: "Unfortunately, I could not complete my service with you. But I am proud of all of you - those who have fallen and those who continue to serve. You are all heroes who will go down in Georgian history."

A roadside bomb struck a minivan in Helmand at about 1 a.m., killing eight civilians. Until then, American commanders had said the province was relatively quiet after the massacre, unlike Panjwai, the district in Kandahar where it occurred. Militants there attacked a memorial service for the 16 victims on Tuesday when an Afghan government delegation was present, firing machine guns and assault rifles from their motorcycles and killing at least one Afghan soldier; a motorcycle bomb went off Wednesday near where the same delegation was staying in Kandahar City, killing a security officer.

Mr. Panetta told reporters on his plane on Monday that the killings in Panjwai were a horrific part of the decade-old conflict.

"War is hell," he said. "These kinds of events and incidents are going to take place, they've taken place in any war, they're terrible events, and this is not the first of those events, and it probably will not be the last."