US President Barack Obama has promised that international forces will not "rush for the exits" in Afghanistan, after an American soldier was accused of murdering 16 civilians.Mr Obama said foreign troops must be withdrawn in a responsible way.
The killings in Kandahar province have strained relations between Afghans and foreign forces.
US Defence Secretary Leon Panetta says the suspect could face the death penalty, if found guilty.
Mr Panetta said that the intention was to try the case in a US military court.
Asked whether the soldier, who gave himself up, had confessed to the alleged crimes, the US defence secretary said: "I suspect that that was the case."
Mr Obama told local CBS station KDKA that the shooting was "absolutely heartbreaking and tragic".
When asked if the incident had made him think that the troop withdrawal should be quickened up, he said: "It makes me more determined to make sure we're getting our troops home."
He added: "What we don't want to do is to do it in a way that is just a rush for the exits."
Mr Obama said that international forces had to make sure the Afghans could secure their borders and stop al-Qaeda from getting back into the country.
Afghan MPs passed a motion earlier saying Afghans had run out of patience.The Taliban has promised revenge attacks. But a tribal elder told the BBC that he would not be calling for protests.
Anti-US sentiment is already high after soldiers burned some copies of the Koran at a Nato base in Kabul last month, sparking deadly riots across the country.
'Turned himself in' Details about the shootings are still unclear, but the American soldier left his base in the southern province of Kandahar in the early hours of Sunday and went on a rampage in nearby villages.
Locals told reporters how they cowered in fear as the man made his way from door to door, trying to get into their houses.
"I saw a man, he dragged a woman by her hair and banged her head repeatedly against the wall. She didn't say a word," one witness said.
He broke into three houses and killed 16 people, most of them women and children. He then burned their bodies, according to reports.
The US defence secretary gave this account of events:
"He went out in the early morning and went to these homes and fired on these families. And then at some point after that, came back to the forward operating base and basically turned himself in, told individuals what had happened."
Pentagon officials said they would not release his name while the investigation was going on.
Reports said the soldier was in his 30s with three children.
He had been deployed to Afghanistan in December for his first tour of duty there after serving three times in Iraq.