Robert Bales shooting trial puts thorny issue of US troop immunity centre stage, with Hamid Karzai hoping to wring tough concessions

Afghanistan and the US have opened talks to keep American troops in the country after most Nato forces go home in 2014, but the thorny question of immunity for American soldiers, which in effect ended the US role in Iraq last year, is likely to prove a stumbling block.

The issue has been thrown into sharp relief by the Seattle trial of the US army staff sergeant Robert Bales, who is accused of the massacring 16 Afghan civilians, mostly women and children, during a shooting spree at their homes in March. US prosecutors are seeking the death penalty but many Afghans, including some of the victims' relatives, want to see him brought before one of their own courts.

"Immunity [for US soldiers] is going to be challenging," said one western official as talks on the bilateral security agreement started late last week. The issue has been set aside in early negotiations, US and Afghan officials said, because the intensity of the clash between Washington's desire to protect its soldiers and the Afghan government's desire to control trial and punishment of any future offenders.

"To be frank, I do not see a way around this. Neither side looks as if they would budge," said Thomas Ruttig, director of the Afghanistan Analysts Network. "Particularly for the US, this (waiving immunity) would be unprecedented. The Afghan government might use it to get other concessions out of the US, but I am not sure what they are aiming at."

The Afghan president, Hamid Karzai, a tough negotiator who has tended to win concessions, said last month the question of protections for US soldiers could be a problem in talks. "Afghanistan wants a strategic pact with US but will seriously consider the red lines," said his spokesman, Aimal Faizi. "The most important issue for Afghanistan is its national sovereignty."

Karzai is possibly betting that the US needs Afghan bases to strike at radical groups hiding along the lawless, mountainous border with Pakistan, and to help peer into Iran's eastern regions. Al-Qaida has made a comeback in Afghanistan, despite the death of its former leader, Osama bin Laden, the commander of US and Nato forces, General John Allen, admitted recently. "We do not want al-Qaida to feel as though [the group] can put down roots here," he told CBS news

Even so, the US is far readier to walk away from Afghanistan than it once was, as the domestic economy sputters and interest in the war fades among voters. The Afghan government cannot survive without US financial and military support in some form, western diplomats and officials have said, and Karzai has not yet fully grasped the shift in dynamics.

There is little question that without help Kabul would struggle. Up to 90% of the national budget is financed by foreign aid, and the Afghan police and army still lack vital skills, from bomb-disposal teams, intelligence, and air support to medical care for injured soldiers.

However, Karzai speaks for many Afghans who would prefer US cash to troops, and even argue that a lasting foreign military presence could give insurgents an excuse to dodge peace talks that are viewed by many as the best hope for ending decades of conflict.

"If the foreigners take home their forces, there will be no reason for theTaliban to send people in the name of jihad," said Allah Gul Mujahed, a conservative member of parliament from the capital, Kabul, who was once with the mujahideen fighting Soviet forces.

Many Afghans were unhappy that Bales had been taken to America and would not accept a deal that enshrined similar protections, he added. "We want everything to be under Afghan law."

Additional reporting by Mokhtar Amiri