U.S. officials worked quickly to calm tensions after an American service member in Kandahar province opened fire on Afghan civilians Sunday, killing at least sixteen.
President Obama said he was "deeply saddened" by news of the attack, in a released statement.
He said the shooting was "tragic and shocking, and does not represent the exceptional character of our military and the respect that the United States has for the people of Afghanistan."
The White House said Obama also spoke to Afghan President Hamid Karzai about the incident and "extended his condolences to the people of Afghanistan, and made clear his Administration's commitment to establish the facts as quickly as possible and to hold fully accountable anyone responsible," according to a readout of the call.
The incident comes at a critical time in U.S.-Afghan relations. Last month, the accidental burnings of Qurans by American troops at an air base sparked a week of violence, killing six Americans and over 30 Afghans. Two U.S. officers were shot by an Afghan colleague within the Interior ministry building, amid those protests.
In a written statement, Secretary of Defense Leon Panetta said he "spoke to President Karzai to offer my deepest condolences and profound regret for the tragic incident in Kandahar province that resulted in the loss of life and injuries to innocent Afghan civilians, including women and children.”
Panetta said a "full investigation is already underway" and said he offered "Karzai my assurances that we will bring those responsible to justice. We will spare no effort in getting the facts as quickly as possible, and we will hold any perpetrator who is responsible for this violence fully accountable under the law."
Panetta said he assured Karzai that "the American people share the outrage," felt by Afghans over the incident.
The commander of the International Security Assistance Force (ISAF), Gen. John R. Allen, similarly said he was "shocked and saddened" by the attack and pledged a “rapid and thorough investigation.”
Reports said the soldier suspected in the attack, who had been captured by Afghan security forces and handed over to the U.S. military, was being held at a NATO base.
"We will maintain custody of the U.S. service member alleged to have perpetrated this attack. And we will cooperate fully with local Afghan authorities as we ascertain all the facts," Gen. Allen said in his statement.
"This deeply appalling incident in no way represents the values of ISAF and coalition troops or the abiding respect we feel for the Afghan people," he added.
NATO and Afghan officials did not reveal the identity of the suspected shooter or victims, but indicated that the dead included women and children.
Last month, Republicans hammered Obama for apologizing to Karzai in a letter in which he called the Quran burnings an “inadvertent” error, but on Sunday, leaders and lawmakers from both sides of the aisle quickly condemned the shooting rampage.
Senate Majority Leader Harry Reid (D-Nev.) said the incident "was absolutely wrong."
“Our hearts go out to these innocent people,” he said during an interview on CNN's "State of the Union," adding that the incident is “just not a good situation.”
Sen. John McCain, (R-Ariz.) called the attack "terrible."
"It's one of those things that you cannot explain except to extend your deepest sympathy to those victims and see that justice is done," he said on "Fox News Sunday."
McCain though cautioned that the tragedy should not hasten a U.S. withdrawal from Afghanistan, arguing that the mission still required a strong commitment from Washington.
"I understand the frustration, and I understand the anger and the sorrow. I also understand and we should not forget that the attacks on the United States of America on 9-11 originated in Afghanistan," he said.
McCain said that if the situation in Afghanistan deteriorated into chaos, the country could "easily" become a new launching pad for al Qaeda attacks.
"That was, is, still our goal as it was the day we went in," he added about preventing Afghanistan from being used to attack the U.S.
GOP presidential hopeful and former House Speaker Newt Gingrich (Ga.) expressed skepticism about the U.S. mission's chances for success in Afghanistan.
"I reached a conclusion frankly about the entire region that is much more pessimistic than Washington's official position," said Gingrich also on Fox. "I think it's going to get substantially worse, not better. And I think that we are risking young men and women in a mission that may frankly not be doable."
Gingrich said the military must investigate the shooting and "convince the people of Afghanistan that justice will be done and we are not going to tolerate that kind of thing."
This story was published at 7:02 a.m. and has been updated.