Kabul, Afghanistan (CNN) -- An American soldier went on a house-to-house shooting spree in two villages in southern Afghanistan early Sunday, Afghan officials said, killing 16 people in what Afghanistan's president called an "unforgivable" crime. NATO's International Security Assistance Force said the soldier acted alone and turned himself in after opening fire on civilians. U.S. President Barack Obama called the killings "tragic and shocking," and offered his condolences to the Afghan people in a phone call to his counterpart in Kabul, Hamid Karzai, the White House said. But the attack is likely to further more anger at international forces following deadly riots over the burning of Qurans by U.S. troops.
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NEW: A military official says the suspect is from Joint Base Lewis-McChord in Washington state
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Afghan troops spotted the soldier leaving his outpost, ISAF officials say
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"We call this an intentional act," Karzai says
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Obama offers sympathy for "tragic and shocking" killings
@placeholder officials from Obama down called the burning an accident and apologized for it, but riots left dozens dead, including six American troops.