KABUL, Afghanistan – The Taliban is vowing revenge against the U.S. after an American soldier allegedly shot and killed 16 Afghan civilians in a Sunday rampage.
In a statement on their website, the militant group promised to "take revenge from the invaders and the savage murderers for every single martyr."
They added "American savages" committed the "blood-soaked and inhumane crime."
"If the perpetrators of this massacre were in fact mentally ill then this testifies to yet another moral transgression by the American military because they are arming lunatics in Afghanistan who turn their weapons against the defenseless Afghans without giving a second thought," the statement said.
Afghan officials reported nine of the 16 victims were children and three were women. They said some of the bodies were also found to be charred.
The veteran American army staff sergeant allegedly left his base in the Panjway district of Kandahar province and walked about a mile to a nearby village, where he went on a house-to-house rampage, methodically shooting Afghan civilians.
U.S.-led forces in Afghanistan stepped up security following the shootings out of concern about retaliatory attacks. The U.S. Embassy has also warned American citizens in Afghanistan about the possibility of reprisals.
The Taliban claimed responsibility for several attacks last month that the group said were retaliation for the Americans burning Korans. Afghan forces also turned their guns on their supposed allies, killing six U.S. troops as violent protests wracked the country.
It's unclear whether there will be a similar response to Sunday's shootings. But the attack will likely spark even greater distrust between Washington and Kabul and fuel questions in both countries about why American troops are still fighting in Afghanistan after 10 years of conflict and the killing of Usama bin Laden.
Pentagon Spokesman Capt. John Kirby told Fox News in an interview Sunday that the shooter is in his mid-thirties and is a father. He was deployed to Iraq twice, but this was his first time being deployed to Afghanistan.
He is based out of Joint Base Lewis-McChord in Washington state, a base that was named "most troubled base in the military" in 2010 by Stars and Stripes magazine.
Kirby said the soldier is in custody and is being questioned by investigators.
Meanwhile, Afghan civilians and local lawmakers say they have their doubts as to whether a single soldier could have committed the massacre alone.
Abdul Rahim Ayubi, a lawmaker from Kandahar province, said the houses that were attacked were over a mile apart, raising questions about how a single soldier could have carried out all of the shootings.
"It is not possible for only one American soldier to come out of his base, kill a number of people far away, burn the bodies, go to another house and kill civilians there, then walk at least 2 kilometers and enter another house, kill civilians and burn them," said Ayubi.
Abdul Ghani, a local councilman in Panjwai district, said local villagers reported seeing two groups of soldiers.
"The villagers said they were hearing machine gun fire and pistol fire from different directions," said Ghani.
However, Kirby says they are "pretty confident" there was only one attacker.
"When it was noticed that the individual left the outpost, it was noticed and reported up the chain of command," he said. "The command did exactly the right thing. They took accounting of everybody they had at that outpost to make sure they knew were everybody was and there was only one person missing. That's how we know there really was only one individual involved in this."
In a statement released Sunday by the White House, Obama said, "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."
"I gave (Afghan) President (Hamid) Karzai my assurances that we will bring those responsible to justice," Panetta said in a statement. "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."
NATO officials apologized for the shootings but did not confirm that anyone was killed, referring instead to reports of deaths.
"I wish to convey my profound regrets and dismay at the actions apparently taken by one coalition member in Kandahar province, said a statement from Lt. Gen. Adrian Bradshaw, the deputy commander of NATO forces in Afghanistan.
"One of our soldiers is reported to have killed and injured a number of civilians in villages adjacent to his base. I cannot explain the motivation behind such callous acts, but they were in no way part of authorized ISAF military activity," he said, using the abbreviation for NATO's International Security Assistance Force.
The top commander in Afghanistan, Gen. John R. Allen, issued a statement saying that he is "absolutely dedicated to making sure that anyone who is found to have committed wrongdoing is held fully accountable."
The head of the ISAF added that he was "shocked and saddened to hear" about the incident and offered his "profound regret and deepest condolences to the victims and their families."
"I pledge to all the noble people of Afghanistan my commitment to a rapid and thorough investigation," Allen said, adding that the U.S. will maintain custody of the service member, provide medical care to injured Afghans and "cooperate fully with local Afghan authorities as we ascertain all the facts."
"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. Nor does it impugn or diminish the spirit of cooperation and partnership we have worked so hard to foster with the Afghan National Security Forces," he added.
The U.S. Embassy in Kabul tweeted videotaped condolences in the primary languages of Pashto and Dari. It also warned Americans in the country to beware of the "risk of anti-American feelings and protests in coming days, especially in eastern and southern provinces."
"U.S. citizens in Afghanistan should remain vigilant and avoid areas where Westerners congregate. Avoid large public gatherings or demonstrations. Past demonstrations in Afghanistan have escalated into violent attacks on Western targets of opportunity.
"Do not discuss travel plans or other personal matters with strangers, or in public. Be alert and aware of your surroundings, and always travel with mobile phones or appropriate communication equipment," the warning reads.
Karzai called the attacks an "assassination" and angrily demanded an explanation. Karzai said he spoke with a 15-year-old boy named Rafiullah who was shot in the leg during the incident. The boy described how an American soldier entered his house in the middle of the night, woke up his family and began shooting them.
"This is an assassination, an intentional killing of innocent civilians and cannot be forgiven," Karzai said in a statement that is sure to incite more violence.
As violence erupts, U.S. officials have debated a faster exit strategy from Afghanistan, which is supposed to be left to fend for itself by 2014. In anticipation of that departure, the U.S. and Afghan governments signed a memorandum of understanding recently about the transfer of Afghan detainees to Afghan control -- a key step toward an eventual strategic partnership to govern U.S. forces in the country.
Sen. John McCain, the ranking Republican on the Senate Armed Services Committee, said the alleged incident cannot be explained "except to extend your deepest sympathy to those victims and see that justice is done."
But, he added, the U.S. is in Afghanistan because that's where the attacks of Sept. 11, 2001, originated.
"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. That is still our goal, as it was the day we went in," McCain said.
Panjawi, the town where the alleged shootings occurred, is inside a rural Taliban stronghold, and is just south of the birthplace of the militant group's senior leaders, including chief Mullah Omar. Panjawi is a launching point for attacks on neighboring Kandahar City and is a key to securing the province, one of the most difficult battlegrounds in the country.
Newscore and The Associated Press contributed to this report.