KANDAHAR, Afghanistan (AP) -- An Afghan youth recounted on Monday the terrifying scene in his home as a lone U.S. soldier moved stealthily through it during a killing spree, then crouched down and shot his father in the thigh as he stepped out of the bedroom.

The soldier, now in U.S. custody, is accused of killing 16 Afghan civilians in their homes in the middle of the night between Saturday and Sunday and then burning some of their corpses. Afghan President Hamid Karzai said nine of those killed were children and three were women.

"He was walking around taking up positions in the house - in two or three places like he was searching," said 26-year-old witness Mohammad Zahir, who watched the gunman while hiding in another room. "He was on his knees when he shot my father" in the thigh, he told The Associated Press. His father was wounded but survived.

Even before the shootings, anti-Americanism was already boiling in Afghanistan over U.S. troops burning Muslim holy books, including Qurans, last month on an American base. The burnings came to light soon after a video purporting to show four Marines urinating on Taliban corpses was posted on the Internet in January.

Now, another wave of anti-foreigner hatred could threaten the entire future of the U.S.-led coalition's mission in Afghanistan. The recent events have not only infuriated Afghanistan's people and leaders, but have also raised doubts among U.S. political figures that the long and costly war is worth the sacrifice in lives and money.

Zahir recounted the harrowing scene in his family home when the soldier came in before dawn.

"I heard a gunshot. When I came out of my room, somebody entered our house. He was in a NATO forces uniform. I didn't see his face because it was dark," he said.

Zahir said he quickly went into another room in the house, where animals are penned.

"After that, I saw him moving to different areas of the house - like he was searching," he said.

His father, unarmed, then took a few steps out of his bedroom door, Zahir recalled.

"He was not holding anything - not even a cup of tea," Zahir said. Then he fired.

"My mother was pulling my father into the room. I put a cloth on his wound," he said.

After the gunman left, Zahir said he heard gunshots near the house again. He stayed in hiding for a few minutes to make sure he was gone.

The shooting rampage unfolded in two villages near a U.S. base in southern Kandahar province. An enraged Karzai called it "an assassination, an intentional killing of innocent civilians" that cannot be forgiven. He demanded an explanation from Washington.

Tensions between Afghanistan and the United States rocketed last month after word of the Quran burnings got out. President Barack Obama said the burnings were a mistake and apologized.

But the strains had appeared to be easing as recently as Friday, when the two governments signed a memorandum of understanding 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.

In Afghanistan's parliament on Monday, however, lawmakers called for a halt to negotiations on the strategic partnership document until it is clear that soldier behind the shooting rampage is facing justice in Afghanistan.

"We said to Karzai: If you sign that document, you are betraying your country," said Shikiba Ashimi, a parliamentarian from Kandahar. "The U.S. should be very careful. It is sabotaging the atmosphere of this strategic partnership."

Still the public response to the shootings so far has been calmer than the six days of violent protests and clashes that erupted after Qurans were burned at Bagram Air Field. There were no signs of protests Monday.

Afghan forces also turned their guns on their supposed allies in the aftermath of the Quran burnings, killing six U.S. troops.

The Taliban vowed revenge. It also claimed responsibility for several attacks last month that the group said were retaliation for the Americans burning Qurans.

The al-Qaida-linked militant group said in a statement on their website that "sick-minded American savages" committed the "blood-soaked and inhumane crime" in a rural region that is the cradle of the Taliban and where coalition forces have fought for control for years.

U.S.-led forces in Afghanistan have 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. As standard practice, the coalition increased security following the shootings out of concern about retaliatory attacks, said German Brig. Gen. Carsten Jacobson, a coalition spokesman.

The suspect in the shootings, who is in U.S. military custody, is a staff sergeant who has been in the military for 11 years. He is married with two children. He served three tours in Iraq and began his first deployment to Afghanistan in December, according to a senior U.S. official.

He is from Joint Base Lewis-McChord, Wash., and was assigned to support a special operations unit of either Green Berets or Navy SEALs engaged in a village stability operation, said a U.S. official, speaking on condition of anonymity because the investigation is still ongoing. Special operations troops pair with local residents chosen by village elders to become essentially a sanctioned, armed neighborhood watch.

Two U.S. defense officials said an investigation has been started by the Army Criminal Investigation Division, but that it was too soon to say when any charges might be filed. They spoke on condition of anonymity because they were not authorized to speak about the issue.

The Afghan Defense Ministry said the gunman left the base in Panjwai district and walked about one mile (1,800 meters) to Balandi village. Villagers described how they cowered in fear around 3 a.m. as gunshots rang out and the soldier roamed from house to house, firing on those inside. They said he entered three homes in all and set fire to some of the bodies after he killed them.

Eleven of the 12 civilians killed in Balandi were from the same family. The remaining victim was a neighbor.

From Balandi, the gunman walked roughly one mile to the village of Alkozai, which was only about 500 meters from the American military base. There the gunman killed four people in one house and then moved to Zahir's house, where he shot his father in the leg.

U.S. officials said initial reports indicated that the soldier returned to his base after the shootings and turned himself in.

Some Afghan officials and local villagers expressed doubt that a single U.S. soldier could have carried out all the killings and burned the bodies afterward.

"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 Abdul Rahim Ayubi, a lawmaker from Kandahar province who visited the area on Monday.

Some villagers also told officials there were multiple soldiers and heard shooting from different directions. But many others said they only saw a single soldier.

Lt. Col. Jimmie Cummings, another spokesman for the coalition, insisted there was only one gunman.

"There's no indication that there was more than one shooter," he said.

Agha Lalia, member of the Kandahar provincial council who is from Panjwai district, said he talked to two people who were injured in the shooting at a hospital at Kandahar Air Field, where they are being treated by coalition medical personnel. Both said they only saw one soldier shooting.

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Associated Press writers Rahim Faiez, Amir Shah, Heidi Vogt and Deb Riechmann in Kabul and Pauline Jelinek in Washington contributed to this report.

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