Washington (CNN) -- Condolences, calls for justice and questions arose from across the political spectrum Sunday in response to reports that a U.S. soldier shot to death 16 civilians in Afghanistan.
President Barack Obama said he was "deeply saddened" by the reported killings and offered condolences to families and loved ones of the victims "and to the people of Afghanistan, who have endured too much violence and suffering."
"This incident is 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," Obama said in a statement that endorsed the announcement by Defense Secretary Leon Panetta of an investigation.
Obama also called Afghan President Hamid Karzai to "express his shock and sadness" over what happened and reaffirm "our deep respect for the Afghan people and the bonds between our two countries," the White House said in a statement.
"A full investigation is already underway," Panetta said in an earlier statement that condemned the violence and expressed shock and sadness at the alletged involvement of a U.S. combatant. "A suspect is in custody, and I gave President 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."
The killings in Kandahar Province follow a recent outbreak of anti-U.S. violence in Afghanistan over the burning of Qurans by U.S. troops last month, and appeared certain to again inflame tensions as U.S.-led NATO forces continue the transition toward ending the Afghanistan mission in 2014.
"The murdering of innocent people intentionally by an American soldier is an act of terror that is unforgivable," Karzai said Sunday.
Conservative Republicans who have challenged Obama's steps toward ending the Afghanistan mission said on Sunday talk shows that justice must be done, but the goal of preventing Afghanistan from again becoming a terrorist haven remained the focus.
"This is tragic and will be investigated, and that soldier will be held accountable for his actions under the military justice system," Sen. Lindsey Graham of South Carolina said on the ABC program "This Week with George Stephanopoulos." "Unfortunately, these things happen in war."
Instead of hastening a U.S. departure, the proper response is to continue preparing Afghan security forces to assume a greater role while negotiating a strategic partnership with the government that would include some U.S. resources staying on past 2014 in order to "stop this narrative that we're leaving," Graham said.
"We can win this thing. We can get it right," Graham said. "I will support the president when he does the right thing."
Another conservative, Arizona Sen. John McCain, called the shootings "a terrible situation."
"It is one of those things that you cannot explain except to extend your deepest sympathy to those victims and see that justice is done," McCain said on "Fox News Sunday."
At the same time, he cited recent progress in talks on a strategic partnership with Afghanistan as a step in the right direction while noting other challenges facing the country, including government corruption and safe haven in Pakistan for insurgents.
Republican presidential hopeful Newt Gingrich, meanwhile, called for condolences to the families and possible compensation for their losses in an effort to make clear a moral distinction between the U.S. forces and their enemies, described by Gingrich as terrorists "in the business worldwide of killing the innocent."
Asked if was time for the United States to leave Afghanistan, Gingrich told the CBS program "Face the Nation" that "I think it is."
"I think that we have to reassess the entire region," he said, citing what he called anti-U.S. activities by nations that are supposed to be allies, such as Pakistan.
On Fox, Gingrich said "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 used the issue to plug his policy of immediately opening all U.S. oil reserves to development to end strategic dependency on the entire Middle East region.
"We need to decide that we're going to produce our own oil and we're going to frankly be capable of surviving without having to define or dominate the region, because I don't think we have the will power or the capacity to do the things you have to do to fundamentally change the region," Gingrich said.
McCain, however, disagreed with any talk of speeding up plans to end the Afghanistan mission.
"I understand the frustration and I understand the anger and the sorrow," McCain said on Fox. "I also understand, and we should not forget, the attacks on the United States of America in 9/11 originated in Afghanistan. And if Afghanistan dissolved into a situation where the Taliban were able to take over or a chaotic situation, it could easily return to an al Qaeda base for attacks on the United States of America."
On the Democratic side, Senate Majority Leader Harry Reid of Nevada said the shootings showed "we're on the right track to get out of Afghanistan just as soon as we can."
"One of our soldiers went into a couple of homes and just killed people at random -- very very sad, especially following that incident dealing with the Qurans," Reid said on CNN's "State of the Union." "It's just not a good situation. Our troops are under such tremendous pressure in Afghanistan. It's a war unlike no other war we've been involved in, but no one can condone or make any suggestion that what he did was right. It was absolutely wrong."
On CBS, Obama campaign adviser Robert Gibbs said called it "a deeply regrettable incident."
"Our job is to do as much as we can to train the Afghans to secure and protect their own country and to continue the transition of giving them that responsibility so that we can bring our men and woman home," said Gibbs, the former White House press secretary to Obama.
CNN's Candy Crowley, Joshua Levs and Emily Schultze contributed to this report.