The US defence secretary has arrived in Afghanistan to meet with troops, commanders and Afghan government officials just days after a US soldier went on a killing spree  that left 16 Afghan villagers dead.

While US officials said the trip was planned months ago, Leon Panetta's arrival on Wednesday propelled him into the centre of escalating anti-US sentiment and set the stage for some difficult discussions with Afghan leaders.

Panetta's two-day visit is scheduled to include meetings with Afghan President Hamid Karzai, Afghan defence officials and provincial leaders, as well as routine discussions with his commanders on the ground.

A stolen vehicle was driven onto the runway ramp at about the same time as Panetta's plane was landing, George Little, a Pentagon spokesman, said.

The vehicle caught fire, but Little denied it had exploded.

"The secretary, we believe, was never in danger," he said

The Afghan driver is being treated for burns, as another Pentagon spokesman said it was unclear whether he was attempting to attack Panetta's party.

Speaking to coalition and Afghan troops in southern Helmand province, Panetta acknowledged the Quran burning, Sunday's killings and  attacks on coalition troops by Afghan soldiers had posed difficult challenges, but said the strategy was still on track.

"Each of these incidents is deeply troubling. We will not allow individual incidents to undermine our resolve," he said.

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"We will be tested, we will be challenged by the enemy, by ourselves and by the hell of war itself," Panetta added.

The US marines who gathered at the tent to hear Panetta were asked to leave their weapons outside, media reports suggested, a sign of nervousness in the wake of the recent events.

The US military has detained an army staff sergeant in connection with Sunday's killings.

Senior US officials are investigating what caused the soldier to go on a shooting spree after leaving his base in southern Afghanistan, apparently heavily-armed and carrying night-vision equipment.

Officials confirmed that the soldier was being detained in Kandahar and that the military was treating at least five wounded people.

Bomb blasts

Even before the shootings, anti-US sentiment was already on the rise in Afghanistan after reports emerged that copies of  the Quran were burned last month at a US-run airbase.

The burnings came to light soon after a video purporting to show four US soldiers urinating on Taliban corpses was posted on the internet in January.

Military commanders have yet to release their final investigation on the Quran burnings, which US officials have apologised for.

Five US service members could face disciplinary action in connection with the incident.

Panetta's agenda is likely to include discussion over the US's planned withdrawal of about 22,000 troops by the second half of the year, including as many as 10,000 troops from Helmand province.

As Panetta was arriving in Helmand, a motorcycle bomb blast in neighbouring Kandahar province killed at least one Afghan security officer and wounded two others.

In another incident on Wednesday, a roadside bomb attack in Helmand killed eight civilians travelling in a minibus, provincial spokesman Daud Ahmadi told AFP news agency.

Source: Agencies