"My personal opinion is I think he had the intent to harm," General Mike Scaparotti told reporters, but refused to see it as an attempt to target Panetta.
"I personally don't believe it had anything to do with the secretary's arrival," he said. There is "no way you can identify one aircraft from the other".
The Afghan interpreter, who was engulfed in flames after crashing the vehicle, had a container of fuel in the car.
"He passed away in medical care this morning," the general said, adding that a coalition soldier injured in the incident was British.
At about the same time Panetta's aircraft was landing at Camp Bastion in southern Helmand province Wednesday, the Afghan "contract employee" hijacked a pick-up truck from a soldier in the US-led coalition force.
He drove the vehicle at high speed before he crashed into a ditch and emerged in flames, Panetta's spokesman George Little told reporters.
Panetta travelled to Afghanistan just days after a US soldier shot dead 16 villagers -- most of them women and children -- in southern Kandahar province in the worst single such incident since the 2001 US-led invasion.
The suspect in the massacre, a US Army sergeant who had served three tours in Iraq, had been flown out of Afghanistan, Pentagon officials said Wednesday, without saying where he was taken.
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