A “rogue” U.S. soldier has killed 15 Afghan civilians and wounded several others in Kandahar province, according to Afghan and NATO officials.

The soldier reportedly entered the civilians' homes and murdered people indiscriminately as they slept, including as many as nine children.

Eleven members of my family are dead, Haji Samad, a local elder, told Agence France-Presse.

NATO described the killings as a deeply regrettable incident and is investigating it in tandem with Afghan authorities.

The soldier, whose identity has not yet been revealed, reportedly turned himself into military authorities.

According to Bernard Smith, a correspondent of Al Jazeera, the soldier apparently walked off his base at 3 a.m., when it was pitch-black.

The soldier went through three separate houses, shooting at people as they slept in their beds. After the soldier shot these people, he turned himself in, Smith said.

It is frankly disastrous. It is not just a disaster for the people who were murdered and killed in their houses, it is disaster for the country, I suspect.”

The deputy commander of NATO forces in Afghanistan, Lt. Gen. Adrian Bradshaw, said in a statement he could not explain the motivation behind such callous acts and added our thoughts and prayers are with those caught in this tragedy.

Similarly, Capt. Justin Brockhoff, a spokesman for the NATO-led International Security Assistance Force, told Al Jazeera:

“This is a horrific incident, and our thoughts are with the families of the affected. ... At this point we do not have an indication. We cannot speculate about the individual's motives.

Afghan President Hamid Karzai is in contact with local political chiefs of Kandahar, which is regarded as the original home of the Taliban.

Western military sources are expecting a huge backlash as groups of Afghans have already assembled near the base where the soldier was stationed.

Just last month, furious demonstrations by Afghans erupted after it was revealed that U.S. soldiers at a base in Kabul burned copies of the Holy Quran. Protests over that incident led to the deaths of at least 30 people and six American troops.

The latest outrage could have grave implications for NATO troops in Afghanistan.

Najeeb Azizi, an Afghan analyst, told Al Jazeera: “It is a very tragic incident in particular because the Afghan and U.S. governments are trying to sign a strategic agreement for a long term.”

Azizi added: “A very bad message the Afghan people are getting -- that if U.S. military remains in Afghanistan beyond 2014 and their attitude and behavior remains the same; of killing innocent civilians, what will be the consequences, and how will the Afghan people respond to it?