By Alex Dobuzinskis

(Reuters) - Well over half of U.S. military veterans who took their own lives in 2014 were aged 50 or older, the government reported on Thursday in a study indicating that combat trauma predating the recent wars in Iraq and Afghanistan still accounts for many veteran suicides.

The U.S. Department of Veterans Affairs analysis, which shows the suicide rate among veterans climbing over the past 15 years, is based on millions of records and is touted as the government's most comprehensive examination of the issue to date.

President Barack Obama has joined veterans groups in singling out as a national priority the prevention of suicide among veterans, who the study says are at a 21 percent greater risk of taking their own lives than other Americans.

The latest report said 20 former members of America's armed forces died of suicide each day on average in 2014, down slightly from a previous study that put the daily average at 22 in 2010.

Of the veterans known to have committed suicide in 2014, the latest year for which such data was available, 65 percent were at least 50 years of age, old enough to have served in the 1990-91 Gulf War, the Vietnam War or previous conflicts.

Fewer members of that age group are likely to have seen combat since the current stretch of U.S. military involvement in Afghanistan and Iraq began in the early 2000s.

"One veteran suicide is one too many, and this collaborative effort provides both updated and comprehensive data that allows us to make better informed decisions on how to prevent this national tragedy," Dr. David Shulkin, the Veterans Affairs under secretary for health, said in a statement.

Fuller analysis and details, including aggregate numbers of veteran suicides on a yearly basis, are expected to be included in a final version of the study to be released next month.

Previous research of the link between battlefield trauma and suicide has found that among veterans who endured combat, those who suffered multiple wounds were at the highest risk of later killing themselves, according to a fact sheet on the website of the Department of Veterans Affairs.

The Department of Veterans Affairs has taken a number of steps to prevent suicides, including the 2007 creation of a telephone hotline.

The latest figures from the department show that since 2001 the rate of suicide among veterans who do not use Veterans Affairs services increased by nearly 39 percent, compared with less than 9 percent for those who did.

(Reporting by Alex Dobuzinskis in Los Angeles; Editing by Steve Gorman and Leslie Adler)