WASHINGTON (AFP) - The man hailed as the deadliest military sniper in US history has been shot to death at a Texas firing range, allegedly by a former soldier with post-traumatic stress disorder.

The death of former Navy Seal Chris Kyle, 38, was confirmed on Sunday by FITCO Cares, a foundation he helped start that worked with returning soldiers to help them cope with PTSD - the same ailment that the alleged shooter is said to have suffered from.

Mr Kyle was also the author of a best-selling book released last year, American Sniper: The Autobiography of the Most Lethal Sniper in US Military History. Mr Kyle was a former US Navy Seal sniper credited with killing more than 150 insurgents in Iraq, during four tours of duty, from 1999 to 2009.

"Chris Kyle helped establish this foundation and we are committed to make sure his memory lives on forever," FITCO said in a eulogy to Kyle posted on its website. "Please pray for all those who loved Chris. He will be forever missed."

The shooting comes amid a raging debate in the United States over gun violence, especially perpetrated by those suffering from mental or emotional illness, after a series of high profile shootings.

The effort to ban assault rifles and high capacity magazines has become a centrepiece of President Barack Obama's second term agenda after a disturbed young man gunned down 20 children and six adults on Dec 14 in the once quiet town of Newtown, Connecticut, in one of the most notorious of the recent shootings.

He died on Saturday at a firing range in Glen Rose, Texas, while helping a soldier recovering from the condition, an ABC affiliate in Dallas, WFAA-TV, reported. A neighbour of Kyle reportedly was also killed.

A suspect has been arrested, and was identified as 25-year-old Eddie Routh.

WFAA-TV quoted investigators as saying Routh is a former Marine who is believed to suffer from PTSD.

The Dallas Morning News wrote that Mr Kyle was awarded two Silver Stars and five Bronze Stars with Valor for his military service.

The marksman wrote in American Sniper that his accuracy as a sniper was so deadly that Iraqi insurgents put a price on his head.

Mr Kyle said in an interview with the daily that he was born for the work of a military marksman. "When I grew up, I only had two dreams," he told the Dallas Morning News about a year ago.

"One was to be a cowboy and another was to be in the military. I grew up extremely patriotic," he said.

"By the time I was 24, I decided it was time to go into the military and try it out. It wasn't exactly the Seals I was looking for at the time. I just wanted to go into the military and be the best." The foundation he led, which said Kyle was survived by a wife and two young children, vowed to continue his work to help soldiers left emotionally and psychologically scarred by combat.

"The FITCO Cares Foundation will always carry the torch to help our brave men and women who have survived combat but are still fighting to survive post traumatic stress disorder," it said.

But it said the group first would have to grieve the loss of its founder.

"My heart is breaking," said Travis Cox, director at FITCO Cares.

"Our foundation, FITCO Cares, this country and most importantly, his wife Taya and their children, lost a dedicated father and husband, a lifelong patriot and an American hero." he said.

"Chris died doing what he filled his heart with passion - serving soldiers struggling with the fight to overcome PTSD. His service, life and premature death will never be in vain."