LOS ANGELES, CA (Catholic Online) - "When Afghan people are killed deliberately by U.S. forces this action is murder and terror and an unforgivable action," Karzai said in a statement.

Senior U.S. officials are still trying to determine what caused the soldier to go on a shooting spree after leaving his base in southern Afghanistan. The soldier was reportedly heavily-armed and carrying night-vision equipment.

The soldier has been detained in Kandahar. The military is medically treating the surviving wounded in the attack, which number at least five.

U.S. President Barack Obama said he was "deeply saddened" by the incident.

"I offer my condolences to the families and loved ones of those who lost their lives, and to the people of Afghanistan, who have endured too much violence and suffering," Obama said in a statement.

One U.S. official said the soldier, an Army staff sergeant, was thought to have acted alone. There are reports that he returned to the base after the shooting and turned himself in.

General John Allen, the top U.S. commander in Afghanistan, issued a statement pledging a "rapid and thorough investigation" into the shooting spree, and said the soldier will remain in custody.

The U.S. embassy in Kabul sent out an alert to its citizens in Afghanistan warning that as a result of the shooting "there is a risk of anti-American feelings and protests in coming days."

Journalists at the scene report that in one house, an elderly woman screamed: "May God kill the only son of Karzai, so he feels what we feel."

The shootings come at an inopportune time for the U.S., in light of the recent violence over the burning of Muslim holy books at a U.S. base was starting to calm down. At least 41 people were killed in that related violence.

The soldier in question reportedly entered three houses near the base and opened fire on civilians.

"We are now being told by the police sources that the US soldier left his base at three o'clock this morning. It would have been pitch-black wherever he walked," Al Jazeera's Bernard Smith reporting from Heart says.

"The soldier went through three separate houses, shooting at people as they slept in their beds. After the soldier shot these people, he turned himself in.

"It is frankly disastrous. It is not just a disaster for the people who were murdered and killed in their houses; it is disaster for the country I suspect."

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