Updated

The U.S. mission in Afghanistan will not change in the wake of an American soldier's alleged attack on Afghan civilians, U.S. officials said Monday amid concerns that the action of a sole shooter could frustrate military efforts, and already prompted efforts to tamp down Afghan anger before it turns to violence.

Secretary of State Hillary Clinton, speaking to reporters at the United Nations on Monday, said the act was "terrible, awful -- I can't even imagine the impact on the families who were subject to this attack and the loss of children in this terrible incident."

But she said while a full investigation is underway and a suspect is in custody, "this terrible incident does not change our steadfast dedication to protecting the Afghan people and to doing everything we can to help build a strong and stable Afghanistan."

White House spokesman Jay Carney said that the U.S. and its NATO allies are still on course to hand over security control to the Afghans at the end of 2014.

The pace of withdrawal will depend on a variety of factors, he said, without indicating whether the weekend incident was among those that would be considered. Carney said President Obama's objective remains focused on "disrupting, dismantling and defeating Al Qaeda."

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"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 Qaeda leaders. That remains his objective. And that has not changed," Carney said.

Carney also would not say whether Obama believes the shooting increases security risks for Americans in Afghanistan. On Sunday, the president called Afghan President Hamid Karzai to express condolences and pledge a thorough investigation.

But Afghanistan's parliament was not appeased, and on Monday called for a stop to negotiations with the U.S. on a strategic partnership until the suspect faces justice.

"The Afghan Parliament issued a resolution today against the butcherly action of the American military against the civilians, and asked the Afghanistan government that the perpetrator of this act should go to court inside Afghanistan," said Shakiba Hashimi, an Afghan member of parliament for the Kandahar province where the shooting took place.

That's not going to happen, U.S. officials say. But the 38-year-old alleged shooter, an Army staff sergeant serving his first tour in Afghanistan after three tours in Iraq, will face justice if he's found responsible for the Sunday morning shooting, which resulted in the deaths of 16 people, including nine children and three women. Reports revealed that some of those bodies were charred.

The sergeant, whose name won't be released until charges are brought, is based out of Fort Lewis McChord in Washington state. It is the same base that served as home to the Army's First Corps headquarters and the 5th Stryker Brigade, from which a kill team of five U.S. soldiers were found guilty of killing civilians and collecting body parts as trophies.

The soldier, who was working with Green Berets to train local police, had reportedly been assigned to the Kandahar province less than six weeks ago.

American troops are on high alert in Afghanistan, as is the Afghan National Security Forces after the Taliban, which has its stronghold in the town where the shootings occurred, pledged revenge.

The attack comes as Americans appear increasingly frustrated with the decade-long war, and new polling shows traditionally supportive Republicans as tired of the war as Democrats who've long opposed the U.S. presence there. An ABC News/Washington Post poll found that 60 percent of Americans say the war wasn't worth fighting.

U.S. Ambassador to Afghanistan Ryan Crocker said he is tired of the war too, but the actions of one rogue soldier should not derail the mission to defeat Al Qaeda.

"We got to be sure an environment never exists where they can regroup and plan more attacks," he said.

The shootings further complicate the goal to have a partnership agreement with the Afghanistan government by May, when a NATO summit convenes in Chicago. But it has also highlighted the president's relative silence about the goals in Afghanistan.

House Armed Services Committee Chairman Buck McKeon agreed that the progress in Afghanistan should not be sidetracked by the weekend's turn of events, but said the president needs to stand up more with a vision..

"Despite what has been a tragic few weeks in Afghanistan, we have vital interests there, and a strategy that can work if our commanders are given the resources and time they need," McKeon, R-Calif., said.

"Now is not the time to abandon hope and freedom's cause, but to persevere. It has been too long since our men and women in uniform, their families, and the American people have heard the president rally the American people to this cause and demonstrate the will to win. With 90,000 men and women serving nobly in harm's way, I believe the commander-in-chief should articulate his support for the mission soon."

Asked about McKeon's argument that President George W. Bush gave more than 40 speeches about Iraq to try to educate the country about the mission while Obama has given just three speeches about Afghanistan, Carney said he "will leave the irony of the comparative there for others to assess."

Carney said the president is focused on national security and ensuring "that every bit of effort expended by American men and women in uniform and our civilian personnel over there is aimed at our strategic objective."

"It is thanks to President Obama that we refocused our strategy on the reason why we were there to begin with, and it is because of that, that we are in the process of drawing down forces in Afghanistan, and in the process of transferring responsibility for security to Afghan security forces, and in the process of supporting an Afghan-led process of reconciliation," Carney said.

He added that he didn't know the accuracy of the claim that Obama issued his apology to Afghan President Hamid Karzai while in a car on his way to his daughter's basketball game, but that may just be the nature of setting up a call with a foreign leader in a very different time zone.