By Brendan O'Brien

MILWAUKEE, Wisconsin (Reuters) - The white supremacist gunman who killed six people at a Sikh temple in Wisconsin died of a self-inflicted gunshot wound to the head, the FBI said on Wednesday.

A police officer shot and wounded the gunman, Wade Page, 40, in the stomach outside the temple in Oak Creek on Sunday, said Teresa Carlson, an FBI special agent in charge.

"Subsequent to that wound, it appears that Page died from a self-inflicted gunshot wound to the head," she told a news conference.

Police had said Page had been shot to death by an officer responding to the attack at the Sikh Temple of Wisconsin in suburban Milwaukee.

Carlson said she had seen a video of the police officer wounding Page with a squad rifle. "It's an amazing shot, and thank goodness," she said.

Federal authorities have said they are treating the attack as a possible act of domestic terrorism. Page, an Army veteran, was a musician who played in white power punk-metal bands. He was armed with a 9mm handgun during the attack.

Turban-wearing Sikhs are often mistaken for Muslims in the United States. The Sikh faith was founded in the Punjab area of India and Pakistan and has an estimated 500,000 or more adherents in the United States.

President Barack Obama called Indian Prime Minister Manmohan Singh to express his condolences over the temple shooting.

Carlson said investigators had not found any motive for the attack, which also wounded four people, including a police officer shot eight or nine times after responding to a 911 call.

The wounded officer, Lieutenant Brian Murphy, is up and walking, Carlson said.

Investigators have conducted more than 100 interviews with Page's relatives, employers and associates, Carlson said. They are also following 101 leads worldwide and have issued 180 federal grand jury subpoenas.

Police have arrested Page's former girlfriend, Misty Cook, on a weapons charge. Carlson said the arrest took place at Cook's Milwaukee home late on Sunday and was unrelated to the shooting investigation.

Police said on Tuesday that a charge of being a felon in possession of a firearm would be sought against Cook, 31.

(This story corrects last paragraph to say that charges would be sought; she has not been charged yet)

(Additional reporting by Paul Thomasch; writing by Ian Simpson; editing by Vicki Allen and Mohammad Zargham)