There are fears of possible reprisal attacks in Afghanistan, after a US soldier went on a deadly shooting spree.
The attack took place in two villages of Kandahar's Panjwai district, with the serviceman going from house to house as he opened fire.
Sixteen civilians, including women and children, were killed.
Barack Obama, the US president, has expressed his deep sadness, and has offered his condolences to the families of the victims.
However, Afghanistan's President Hamid Karzai has called the deaths "international murders".
Al Jazeera's Bernard Smith reports from the capital Kabul.