The Pentagon acknowledged Thursday that a security breach during Defense Secretary Leon E. Panetta’s visit to Afghanistan was much more serious than officials first reported, saying that an Afghan man tried to ram a stolen truck into a group of VIPs who were waiting to greet Panetta just moments after his plane landed at a military base.

The driver set himself on fire Wednesday and apparently tried to ignite containers of gasoline in the cab of the truck as he attempted to run over several high-ranking Marine officers and others who were waiting for Panetta’s plane to park, said Navy Capt. John Kirby, a Pentagon spokesman.

“He took a vehicle by force, drove it onto a ramp, at a high rate of speed, drove it at individuals who had to get out of the way to keep from getting hit by it, and then a flash of smoke and fire [appeared] in the cab,” Kirby told reporters.

The Afghan man was quickly apprehended. He suffered severe burns and died. Panetta’s plane was diverted to another ramp at Camp Bastion, a British installation adjoining the U.S. Marines’ Camp Leatherneck base in the southern province of Helmand.

U.S. military officials withheld news of the attack for 10 hours from reporters who were traveling on the same plane with Panetta, releasing sketchy information about it only after British news media broke the story. The officials tried to play down the seriousness of the incident, saying Panetta was never in danger. They also said Wednesday that they could not confirm that the incident was an attempted attack or even that it was linked to Panetta’s visit.

On Thursday, Panetta also tried to minimize his close brush with danger, saying he did not think the attack was aimed at him.

“I have absolutely no reason to believe that any of this was directed at me,” he told reporters before he left the country. “Whatever happened here was directed at others who were there on the field, not me or my plane or anything associated with me.”

Kirby said the Afghan man, a civilian interpreter who worked on contract for NATO officials, hijacked the truck by force at Camp Bastion 30 minutes before Panetta landed. He said no firearms or detonators were found on the individual or inside the truck but could not rule out that the man had been armed earlier. A British soldier was reported injured when the truck was stolen.

The Pentagon said it could not answer questions about whether Panetta’s security detail had been warned in advance of the security breach on the base or whether an alert had been issued about the stolen truck, saying an investigation was underway.

The Afghan interpreter had burns on more than 70 percent of his body. Kirby said investigators were unable to interview him before he died. The spokesman added that he did not know whether the man made any unsolicited comments or gave any hints about his motive after he was apprehended.

“There’s reason to believe he intended harm,” Kirby said. “We can’t interview him, so I don’t know that we’re going to get much more.”

He said military officials “don’t have any indication that he knew who was on that airplane.” But Kirby said investigators could not rule out that Panetta was the intended target.