KABUL (AFP) - A policeman and two security guards were killed Thursday in an attack on checkpoints set up to protect a road construction site in southern Afghanistan, an official said. A group of armed militants stormed three checkpoints early Thursday on a road project linking the volatile Chora district to Trinkot, the capital of Uruzgan province. The fighting continued for several hours. Two private security guards and one policeman were martyred and one policeman was wounded, provincial spokesman Milad Modaser told AFP. The spokesman said a number of the attackers were killed or wounded in the fighting but could not provide an exact figure. The Taliban were not immediately available to comment but the militants have threatened to kill anyone who participates in projects connected with or funded by the international community or Afghan government. Last month, hundreds of Taliban fighters attacked a road construction site in the eastern province of Paktia, killing 36 workers and guards in one of their worst attacks in months. Meanwhile, an ambush on an armoured vehicle in northern Afghanistan killed one German soldier and wounded another five, German military said in a statement. Their armoured personnel carrier was struck by an improvised explosive device early Thursday outside the city of Kunduz, five days after a suicide bombing claimed the lives of two German soldiers and the regions police chief. Germany has about 5,000 troops serving in Afghanistan with the Nato-led force, in a mission that polls show is deeply unpopular with the public.