White House spokesman Jay Carney said Obama's policy in Afghanistan -- to disrupt, dismantle, and defeat al-Qaida, and help stabilize Afghanistan -- remained in effect and the shooting would not impact the timetable for the withdrawal of U.S. troops by the end of 2014.
"Because, after all, there is one reason why U.S. forces were sent to Afghanistan, and that is because the United States was attacked on Sept. 11, 2001, in a plot that was hatched in Afghanistan by al-Qaida leaders," Carney said during the daily briefing in Washington. "That remains his objective. And that has not changed."
The United States also wants to press forward in its relationship with Afghanistan despite the shooting spree by a U.S. soldier in which 16 civilians, the State Department said.
The attack Sunday presented "another challenge" in the U.S.-Afghanistan relationship, State Department spokesman Mark Toner said during the daily media briefing in Washington, but the United States is "committed to moving forward in the relationship" with Afghanistan.
"We're working on the strategic partnership document, and that work is going to continue," Toner said.
The Taliban vowed Monday to avenge the deaths of 16 civilians allegedly killed by a U.S. Army staff sergeant who went on a shooting rampage near his base. In a statement posted online, Taliban leaders said U.S. forces were "sick-minded American savages" and the Taliban would seek revenge for the "barbaric actions."
The Afghan Parliament called for a public trial for the suspect, accused of killing nine children, three women and four men Sunday in two villages in the Panjwai district, about 15 miles from Kandahar.
"We strongly request the government of America to punish this wild act and have a public trial in front of the people of Afghanistan," Afghan lawmakers said in a statement issued Monday.
The killings, which following deadly riots related to last month's accidental burning of Korans by U.S. troops, raised fears of stepped-up acts of aggression against international forces in Afghanistan.
"There has been … a series of challenges in the relationship and … . This incident in particular is just horrific. It's a terrible tragedy by any measure," Toner said. "But we have to look at the whole relationship and -- and the whole history of our involvement in Afghanistan and what we're trying to accomplish here."
If one looks at the U.S.-Afghanistan relationship as a whole, then "you've got to recognize that we're moving forward, we're committed to the Afghan government and the Afghan people to working and building a stronger relationship," the State Department spokesman said.
He said the U.S. Embassy in Kabul issued an emergency message warning American citizens about the risk of anti-American sentiment and protests in the coming days.
"We haven't seen anything," Toner said, "but we're certainly very much aware that that potential exists."
The shooting suspect acted alone and turned himself in after the spree near his base, officials from NATO's International Security Assistance Force said. He is in U.S. custody.
Karzai called the attack an "unforgivable" crime.
U.S. President Barack Obama called the killings "tragic and shocking" and offered his condolences to the Afghan people in a phone call to Karzai, the White House said.
The suspect, in his mid-30s and on his first deployment to Afghanistan, previously completed tours in Iraq, a U.S. military official told CNN. The suspect is from Joint Base Lewis-McChord in Washington and is assigned to a Special Forces unit.
The attacker's mental stability and medical history are among "the things the investigators are looking at," said Capt. John Kirby, a spokesman for the International Security Assistance Force.
Residents of three villages told The New York Times about the attacks in which a soldier went door to door, breaking into houses on his killing spree. Villagers said the man collected 11 bodies and set them on fire.
Five people were wounded and were being treated at ISAF medical facilities, officials said.
The Times said villagers offered differing accounts about the number of people involved, with some saying more than one person was shooting and others saying the slaughter was carried out by a lone attacker.