Image caption People aged 35-64 accounted for nearly two thirds of of US suicides

The suicide rate among middle-aged Americans rose 28% in a decade, a new report from the Centers for Disease Control (CDC) has found.

Among adults 35-64, white people and American Indians saw the sharpest increases from 1999 to 2010.

The CDC did not investigate causes behind the trend, but noted many suicide prevention programmes were geared towards youths and the elderly.

The report found no significant change among other age groups.

Since 2009, suicide has claimed more Americans than motor vehicle crashes.

There were 38,350 suicides in 2010, making it the nation's 10th leading cause of death, the CDC said.

People aged 35-64 accounted for some 57% of suicides in the US, according to the data.

Overall, the suicide rate among Americans in this age group increased from nearly 14 per 100,000 people in 1999 to almost 18 in 2010, the CDC reported.

Among American Indians, suicides increased 65% from more than 11 per 100,000 to almost 19 in that decade

Suicides by white people increased 40%, from 16 per 100,000 to 22.

Experts are unsure about what caused the increase in suicides to be so disproportionately steep among Native Americans and white people, during a period which spanned the recession.

The sharpest increase in suicides in the study was among 50 to 64-year-olds of all ethnic backgrounds.

Death by firearm was still the most common method of suicide among middle-age Americans, representing 48% of such recorded incidents in 2010.

Hangings overtook drug overdoses in this age group, becoming the second most common method of suicide.