Police have searched the home of a gunman who killed six people at a Sikh temple in southern Wisconsin, looking for clues to his motive.
A police officer called to the scene shot dead the gunman before he could fire on more worshippers as they prepared for Sunday services at the temple in Oak Creek, south of Milwaukee.
Three other people were in hospital with serious injuries, including a police officer who had also responded to the scene.
Authorities said they were treating the attack as an act of domestic terrorism.
The identity of the tall, bald, white suspect in his 40s was not immediately released. The names of the victims also were not made public pending notification of relatives, although members said the president of the congregation and a priest were among the victims.
CNN, citing a law enforcement source involved in the investigation, said the gunman was a US army veteran.
Authorities said the gunman had used a 9mm semi-automatic handgun, which was recovered at the scene. They were trying to track the origin of the weapon.
Wisconsin has some of the most permissive gun laws in the country and passed a law in 2011 allowing citizens to carry a concealed weapon.
Jagjit Singh Kaleka, the brother of the president of the temple, who was among the six Sikhs killed, said he had no idea about the motive for the attack.
"But we know the more assault weapons we distribute the more situations like this we will have," he said. A US ban on certain assault weapons expired in 2004.
Early on Monday, police were searching an apartment at a duplex in the Cudahy district near Milwaukee, presumed to be the home of the gunman. Generators and floodlights were set up along the street and a bomb squad was on the scene.
The attack came just over two weeks after a gunman killed 12 people at a cinema in Aurora, Colorado, where they were watching a screening of The Dark Knight Rises.
In January 2011, a gunman killed six people in an attack on an event held by the then congresswoman Gabrielle Giffords in Tucson, Arizona. Giffords was shot in the head but survived.
American Sikhs say they have often been singled out for harassment, and occasionally violent attack, since the 9/11 attacks. Sikhs are not Muslim but many Americans do not know the difference, members of the Sikh community say.
Some witnesses to the Wisconsin shooting said the suspect had a tattoo marking the attacks on 11 September 2001. Authorities confirmed he had tattoos but said they were not sure exactly what the tattoos illustrated.
There are 500,000 or more Sikhs in the US but the community in Wisconsin is small, with about 2,500 to 3,000 families, said local Sikhs.
The Sikh faith is the fifth largest in the world, with more than 30 million followers. It includes belief in one God and that the goal of life is to lead an exemplary existence.
The temple in Oak Creek was founded in October 1997 and has a congregation of 350 to 400 people.
"These people were going to church. Two weeks ago, it was people going to a movie. When is it going to end?" said Ray Zirkle, who came from Racine, Wisconsin, with his wife to light votive candles near the site of the shooting.
