US President Barack Obama said "soul searching" was needed on how to reduce violence in America after the killings, and Indian Prime Minister Manmohan Singh said he was "deeply shocked and saddened."

Obama ordered flags at government buildings to fly at half-staff until sunset Friday over the Sikh killings.

"I think all of us recognise that these kinds of terrible, tragic events are happening with too much regularity for us not to do some soul-searching and to examine additional ways that we can reduce violence,” Obama told reporters at the White House.

“I think it will be very important for us to reaffirm once again that, in this country, regardless of what we look like, where we come from, who we worship, we are all one people, and we look after one another and we respect one another,” he said.

The Indian-American community held a candlelight vigil late Monday to honor the

dead, at a temple not far from the scene of Sunday's carnage

The dead were identified as Param jit Kaur, a 41-year-old woman, Sita Singh, 41, Ranjit Singh, 49, Satwant Singh Kaleka, 65, Prakash Singh, 39 and Suveg Singh, 84, all men. Singh is a common surname in the Sikh community.

The Indian embassy in Washington said it had been told that four of the six were Indian nationals but did not respond to a request for more details.

The Washington-based Sikh Goalition said there had been "thousands" of incidents of hate crimes, discrimination and profiling against Sikhs since the September 11 attacks of 2001, attributing blame to antiMuslim sentiment.

Religious tradition demands that Sikh Indians wear turbans to cover their uncut hair and sport long beards, which often leads them to be mistaken for Muslims in the United States.