Update (2:30 p.m. EDT): MSNBC is reporting the man set himself on fire, so that would explain why he burned but not the truck. But his intention with the stunt is still unclear.
Update (1:47 p.m. EDT): The incident's starting to look like an attack attempt after all. And the truck didn't explode, it seems, but the driver somehow caught on fire. The Washington Post is reporting that the driver rammed the truck through a fence alongside the runway and is calling the incident an "apparent attempt to attack the plane." AP, meanwhile, has updated its story with a quote from Gary Kolb, a U.S. military spokesman in Afghanistan, who said "It's too early to say right now" whether the incident was an attack. It had previously cited Pentagon spokesman Navy Capt. John Kirby, who said it didn't look like an attack attempt. Kolb also said the truck didn't explode, but that the driver wound up engulfed in flames after crashing his truck into a ditch.
Original: Just as U.S. Secretary of Defense Leon Panetta landed in Afghanistan, someone drove a stolen pickup truck onto the runway and then into a ditch where it exploded, but a Pentagon spokesman said it didn't look like the driver was trying to attack Panetta.
Nobody in Panetta's party was hurt, but the driver was pretty badly burned, the Associated Press reported. The driver apparently works at Camp Bastion, the British air base where Panetta landed, according to The Telegraph. Despite the explosion, investigators didn't find any kind of explosives in the truck, the AP reported. At an unrelated press conference with President Obama, British Prime Minister David Cameron fielded a question on the breaking story. He was still getting "very early details," he said, and promised a full investigation into the incident.