US Defence Secretary Leon Panetta arrives in Afghanistan

US Defence Secretary Leon Panetta arrived in Afghanistan today to meet troops, commanders and Afghan government officials just days after a US soldier allegedly went on a deadly shooting spree.

The visit was planned months ago, long before the weekend rampage in which 16 villagers, including women and children, were killed.

But the trip propels Mr Panetta into the centre of escalating anti-American anger and sets the stage for some difficult discussions with Afghan leaders.

He and other US officials have said the shooting spree should not derail the US and Nato strategy of a gradual withdrawal of troops by the end of 2014. But it has further soured relations with war-weary Afghans, jeopardising the US strategy of working closely with Afghan forces so they can take over their country's security.

There were clear concerns about security in the large tent at Camp Leatherneck where Mr Panetta was due to talk to troops.

Before he came into the hall, Sergeant Major Brandon Hall told the more than 200 Marines to take their weapons outside and leave them there. Afghan troops had already been told not to take their guns in.

"Something has come to light," Sgt Maj Hall told the troops. It was a highly unusual order, and some in the audience said they had never seen that happen before.

Asked about the order, Sgt Maj Hall said all he knew was that "I was told to get the weapons out".

A US defence official said the request was not a reaction to an immediate threat but a decision by the base commander.

The official said it was made out of respect for troops from other countries, such as the Afghans, who are never allowed to take guns into an event. It was not a request from Mr Panetta or his security team, he added.

Mr Panetta met several Afghan provincial leaders, and told them the primary mission was to prepare for the transition to Afghan security control.

He acknowledged that there would continue to be challenges from the enemy as well as issues between US and Afghan allies, but said everyone must remain committed.

The military has detained an Army staff sergeant in connection with Sunday's massacre.

Even before the shootings, anti-Americanism was already high in Afghanistan over US troops burning Muslim holy books, including Korans, last month on an American base. The burnings came to light soon after a video purporting to show four Marines urinating on Taliban corpses was posted on the internet in January.

Military commanders have yet to release their final investigation on the Koran burnings, which US officials say was a mistake. Five US service members could face disciplinary action in connection with the incident.

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

The sessions are likely to touch on America's planned withdrawal of about 22,000 troops by the autumn, including as many as 10,000 Marines from Helmand Province.