PANJWAI, Afghanistan - Stalking from home to home, a US Army sergeant methodically killed at least 16 civilians, nine of them children, in a rural section of southern Afghanistan early Sunday, Afghan and US officials said, igniting fears of a new wave of anti-American hostility.
Residents of three villages in the Panjwai District of Kandahar Province described a terrifying string of attacks in which the soldier, who had walked more than a mile from his base, tried door after door, breaking in to kill within three houses.
At the first, the man gathered 11 bodies, including those of four girls younger than 6, and set fire to them, villagers said.
Coming after a period of deepening public outrage, spurred by the Koran burning by US personnel last month and an earlier video showing US Marines urinating on dead militants, the apparently unprovoked killings added to a feeling of siege here among Western personnel.
Officials described a growing sense of concern over a cascading series of missteps and offenses that has cast doubt on the ability of NATO personnel to carry out their mission and has left troops and trainers increasingly vulnerable to violence by Afghans seeking revenge.
The US military gave few details about the suspected killer other than to describe him as an Army staff sergeant who was acting alone and surrendered himself for arrest.
A senior US military official said the sergeant was attached to an Army unit based at Joint Base Lewis-McChord, near Tacoma, Wash., and that he had been part of what is called a village stabilization operation in Afghanistan, in which teams of Green Berets, supported by other soldiers, try to develop close ties with village elders, organize local police units, and track down Taliban leaders.
The official said the sergeant was not a Green Beret and had been deployed to Iraq or Afghanistan at least once before his current tour of duty.
President Hamid Karzai condemned the attack, calling it in a statement an “inhuman and intentional act’’ and demanding justice.
President Obama and Defense Secretary Leon Panetta called Karzai, expressing condolences and promising thorough investigations.
“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.
US officials in Kabul were scrambling to understand what had happened and appealed for calm.
“The initial reporting that we have at this time indicates there was one shooter, and we have one man in custody,’’ said Lieutenant Colonel Jimmie Cummings, a NATO spokesman.
In Panjwai, a reporter for The New York Times who inspected bodies that had been taken to the nearby US military base counted 16 dead, and saw burns on some of the children’s legs and heads.
“All the family members were killed, the dead put in a room, and blankets were put over the corpses and they were burned,’’ said Anar Gula, an elderly neighbor who rushed to the house after the soldier had left. “We put out the fire.’’
The villagers also brought some of the burned blankets on motorbikes to display at the base, Camp Belambay, in Kandahar, and show that the bodies had been set alight.
Soon, more than 300 people had gathered outside to protest.
At least five other Afghans were wounded in the attacks, officials said, some of them seriously, indicating the death toll could rise.
NATO said several casualties were being treated at a military hospital.
One of the survivors from the attack, Abdul Hadi, 40, said he was at home when a soldier broke down the door.
“My father went out to find out what was happening, and he was killed,’’ he said. “I was trying to go out and find out about the shooting but someone told me not to move, and I was covered by the women in my family in my room, so that is why I survived.’’
Hadi said there was more than one soldier involved in the attack, and at least five other villagers described seeing a number of soldiers, and also a helicopter and flares at the scene.
But that assertion was unconfirmed - other Afghan residents described seeing only one shooter - and it was unclear whether extra troops had been sent out to the village after the attack to catch the suspect.
But in a measure of the mounting levels of mistrust between Afghans and the coalition, many Afghans, including lawmakers and other officials, said they believed the attack had been planned and were incredulous one soldier could have carried out such an attack without help.
In his statement, Karzai said “American forces’’ had entered the houses in Panjwai, but at another point he said the killings were the act of an individual soldier.
Others called for calm. Abdul Hadi Arghandehwal, the minister of economy and the leader of Hezb-e Islami, a major Afghan political party with Islamist leanings, said there would probably be new protests.
But he said the killings should be seen as the act of an individual and not of the United States.
Elsewhere, news of the killings was only spreading slowly.
Other than the protest at the base in Kandahar, there were no immediate signs of the fury that fueled rioting across the country following the burning of Korans by US military personnel in February.
The US Embassy in Kabul, which immediately urged caution among Americans traveling or living in Afghanistan, and the military coalition rushed to head off any further outrage, deploring the attack, offering condolences for the families, and promising the soldier would be brought to justice.
Brigadier General Carsten Jacobson, the NATO spokesman, expressed his “deep sadness’’ and said that while the motive for the attack was not yet clear, it looked like an isolated incident.
“I am not linking this to the recent incidents over the recent days and weeks,’’ he said. “It looks very much like an individual act.’’
Adding to the sense of concern, the killings came two days after an incident in Kapisa Province, in eastern Afghanistan, in which NATO helicopters apparently hunting Taliban insurgents instead fired on civilians, killing four and wounding another three, Afghan officials said. About 1,200 demonstrators marched in protest in Kapisa on Saturday.
The reaction to the Koran-burning revealed the huge cultural gap between the Americans, who saw it as an unfortunate mistake, and the Afghans, who viewed it as a crime and wanted to see those responsible tried as criminals.
But both the Afghans and US officials agreed on the severity of Sunday’s killings, and Jacobson said the case would be aggressively pursued by US legal authorities.
Panjwai, a rural suburb of Kandahar, was traditionally a Taliban stronghold. It was a focus of the US military offensive in 2010 and was the scene of heavy fighting.
The shootings carried some echoes of an incident in March 2007 in eastern Afghanistan, when several Marines opened fire with automatic weapons, killing as many as 19 civilians after a suicide car bomb struck the Marines’ convoy, wounding one Marine.