Cameron and Obama in Afghan exit talks

In a joint article for the Washington Post, the two leaders signalled that the weekend’s shooting incident, in which a US soldier shot 16 Afghan civilians dead, is a reminder that “this remains a difficult mission”.

Although the leaders have stressed in public that there will be no rush to exit in the wake of that incident, they are due tomorrow to agree plans for British and US troops to end their “lead combat role” in Afghanistan by next year.

This would allow allied troops to withdraw into a support role and begin the process of returning home by the previously-agreed target end date of 2014.

Around 33,000 of America’s 90,000-strong force are due to leave Afghanistan in September, and Britain will withdraw 500 of its 9,500 troops.

Unwinnable

Their discussions will take place as a new poll reveals that nearly three quarters of the public believe that the war in Afghanistan is unwinnable.

Last June, 60 per cent of people said that British troops should be withdrawn immediately, but that figure had swelled by 73 per cent this week, the ComRes poll results suggested.

Meanwhile, further details are beginning to emerge of the US staff sergeant implicated in the shooting spree in Kandahar, southern Afghanistan.

A US official has indicated that the serviceman had been treated for a traumatic brain injury suffered in a vehicle rollover in 2010 during a previous deployment in Iraq.

However it is premature to draw conclusions as to whether there is any link between the injury and the shootings, the official added.

Read more: What now for US Afghan mission after Kandahar shootings?