President Hamid Karzai, who is seeking re-election Aug 20, has repeatedly pleaded with foreign forces in the country to avoid civilian deaths.

US General Stanley McChrystal, NATO's commander in Afghanistan, has ordered the allied forces to limit their use of airpower and make protection of Afghan civilians their top priority during anti-Taliban operations.

The UN said in a report released late last month that civilian casualties in Afghanistan increased by 24 percent during the first half of 2009 compared with the same period last year.

Meanwhile, six civilians including two tribal elders were killed when their vehicle was hit by a roadside bomb in the Pachir Agam district of the eastern province of Nangarhar Wednesday, said Ahmad Zia Abdulzai, a spokesman for the provincial governor.

He said the elders along with their four companions were on their way to the district centre to settle a dispute over the construction of a road when the incident occurred. One other civilian was wounded.

No group took responsibility for Wednesday's attack. Taliban militants rely heavily on the use of roadside bombs as part of their campaign against Afghan and the around 100,000 international forces in country.