led troops opened fire on a vehicle in southeastern Afghanistan, killing four unarmed men, the alliance said Tuesday, the latest in series of incidents in recent weeks the United Nations has called disturbing. The issue of civilian casualties caused by foreign forces is an emotive one in Afghanistan and has undermined public support for their presence in the country. In the latest incident, troops fired on the vehicle after it accelerated towards their convoy in Khost province and ignored light signals and warning shots, the NATO-led International Security Assistance Force said in a statement. “The vehicle continued to accelerate. Several rounds were fired in an attempt to disable the vehicle, and finally shots were fired into the vehicle itself,” NATO said in the statement. The statement described the men who had been killed as two “known insurgents” and two “associates,” but a spokesman, Lieutenant-Colonel Todd Vician, said all may have been civilians. The two were described as “insurgents” because they were found in the military's vast bio-metric database, Vician said. Asked if they could have been civilians who were scanned in the database for another reason, Vician said: “I think that's true”. NATO troops keep information about tens of thousands of Afghan men in their bio-metric database for a number of reasons, including those who seek access to military bases. Vician said none of the men were armed and no weapons were found in the car. Since taking command last year, the commander of US and NATO forces, General Stanley McChrystal, has had success in reducing civilian casualties caused by his forces. But recent weeks have seen a spate of such incidents, prompting the new UN envoy in Afghanistan, Staffan de Mistura, to describe it last week as a “disturbing trend”. McChrystal has said highway shootings by his troops, which the military refers to as “escalation of force incidents”, frequently result in deaths of Afghans who posed no threat.