For the past six years, the US government's aid agency, USAID, has tried to install a third turbine to boost the energy output of the Kajaki dam in Afghanistan's Helmand province.

The dam is considered a showcase of the international coalition's efforts in Afghanistan and would provide electricity to up to two million people when operational.

But the installation has been fiercely opposed by the Taliban, with the dam still not working and Chinese contractors fleeing because of security concerns.

In 2008 about 200 people, most of them Afghans, were killed in clashes between the Taliban and a NATO convoy transporting materials to the dam.

US forces guarding the area say that safety has improved since then, while a US company recently earned a $266 million contract to install the turbine and upgrade the plant with a view to it being ready for use by the end of 2014.

But with Afghan forces set to take over from their international counterparts, the future security of the dam remains uncertain.

Al Jazeera's Bernard Smith reports from Helmand province.