The US military said Friday that an attack at a NATO base in Afghanistan this week targeted a top American commander, just as Defense Secretary Leon Panetta flew in for a visit.

After having initially downplayed the incident, officials threw new light on Wednesday's attack at British-run Camp Bastion in Helmand province that showed it was much more serious than initial accounts suggested.

The Afghan attacker, an interpreter who worked at the base, was only minutes away from striking the area where Panetta's aircraft was due to park, officials said.

US Major General Mark Gurganus, the new head of the NATO-led force's southwest regional command, was part of a VIP welcoming party on the tarmac when a hijacked vehicle hurtled towards them at high speed, Pentagon spokesman George Little told reporters travelling with Panetta.

British General Stuart Skeates, deputy commander of the region, also was in the greeting committee, officials said.

"The vehicle was headed in their direction," said a senior defense official, who spoke on condition of anonymity.

The generals and others waiting to greet Panetta then got out of the way while the hijacked vehicle ended up in a ditch near a runway ramp.

The Afghan driver emerged from the car engulfed in flames before he was apprehended, later dying of severe burns early the next day at about 1:30 am local time, according to the official.

The attack occurred at about the same time the Pentagon chief's aircraft was landing shortly after 11:00 am, and the C-17 military transport plane was diverted to a different parking space after learning of the incident.

Security officers "found a gas can and a lighter" in the hijacked vehicle but no components for a homemade bomb, the defense official said.

The new details indicated a possible suicide attack but the International Security Assistance Force (ISAF) judged that it was unclear if the Afghan had intentionally set himself on fire, the official said.

"It remains ISAF's view that it is unlikely that the individual knew that the secretary was on the plane," the official said.

If the attacker's hijacked vehicle had arrived only minutes later where the welcoming party stood, Panetta might have been in harm's way. But the defense official said that scenario was "hypothetical."

It took 10 hours for the Pentagon to confirm the attack on Wednesday and officials have dribbled out confusing details of the attempted airport attack since, insisting initially there was no link to Panetta's arrival but now confirming that the target was indeed the regional US commander.

The incident is sure to fuel concerns about a surge in attacks on Western troops carried out by Afghans being trained to take over security by the end of 2014.

The Afghan assailant worked as an interpreter at Camp Bastion, which adjoins the US base Camp Leatherneck, home to a large contingent of American Marines.

Officials also disclosed that three Afghan nationals, including the attacker's brother and father, had been taken into custody and questioned. The brother and father also worked as interpreters for NATO forces at the military complex.

The hijacked vehicle, which belonged to a British soldier, was not a pickup truck as initial accounts stated but a four-wheel drive Toyota Hi-Lux, an official said.

A British soldier in the International Security Assistance Force (ISAF) who was run over during the hijacking was in "stable" condition, he added.

Panetta sought to downplay the incident at a news conference on Thursday in Kabul, after he held talks with President Hamid Karzai billed as a chance to defuse outrage over a massacre of civilians by a rogue US soldier.

"I have absolutely no reason to believe that this was directed at me," he said of the attack, but added: "This is a war area" and "we're going to get these kind of incidents".

Just hours after the attack on the airfield, Garganus, a two-star general, made no mention of the incident when he briefed reporters.

"You can't get a whole lot safer than right here, when you're surrounded by everybody else on the base," he said, insisting there had been no violent reaction since the US soldier's shooting rampage in nearby Kandahar.