Protesters angry over Qur'an burnings by American troops lobbed grenades at a U.S. base in northern Afghanistan and clashed with police and troops in a day of violence that left seven international troops wounded and two Afghans dead.

U.S. military commanders in Afghanistan have assigned 'guardian angels' — troops that watch over their comrades even as they sleep — and have ordered a series of other increased security measures to protect troops against possible attacks by rogue Afghans.