NATO troops killed four civilians and injured 18 other passengers when they opened fire on a bus in the southern Afghanistan province of Kandahar on Monday. The troops, who belonged to NATO's International Security Assistance Force, fired on the bus after it refused to stop for a peacekeeping patrol.

NATO has since offered its apologies for the incident. However, that did not restrain Afghan President Hamid Karzai from delivering a harsh criticism of the troops. He said there could be no justification for opening fire on a public bus.

Following the attack, 200 people took to the streets of the provincial capital Kandahar to demonstrate. They set car tyres on fire and shouted slogans against the government of the United States, President Karzai and the Afghan government.

A few hours later, three armed Taliban militants tried to storm the office of Afghanistan's secret service in Kandahar. This led to an exchange of gunfire with security forces.