Nearly one in 10 American soldiers who served in Iraq were diagnosed with post-traumatic stress disorder, most after witnessing death or participating in combat, a study said on Tuesday.

Mental health screening of veterans showed 21,620 out of 222,620 returning from Iraq and assessed over the year ending April 30, 2004, suffered from post-traumatic stress - a disorder that can lead to nightmares, flashbacks and delusional thinking.

Overall, 19.1 percent of soldiers and Marines who returned from Iraq met the military’s “risk criteria for a mental health concern” such as post-traumatic stress or depression, compared to 11.3 percent among veterans who served in Afghanistan and 8.5 percent from deployments elsewhere, the report published in the Journal of the American Medical Association said.

The survey covered 222,620 returning veterans from Iraq, 16,318 from Afghanistan and 64,967 from other deployments.

“A higher percentage of those soldiers (returning from Iraq) report mental health concerns and use mental health services when they get home ... compared to soldiers who are returning from deployment to Afghanistan or other locations,” said study author Col. Charles Hoge of Walter Reed Army Institute of Research in Silver Spring, Maryland.

Of those diagnosed with post-traumatic stress, 80 percent said they had witnessed people being killed or wounded or had participated in combat and fired their weapon, the report said. Of those not diagnosed, half had experienced violence or combat.

Post-traumatic stress disorder and other combat-related mental problems can lead to family strife, divorce, alcohol and substance abuse, and unemployment, Hoge said.

While one in five veterans returning from Iraq reported concerns about their mental health, about one-third ultimately went for at least one session to be evaluated or counseled, the study said.

“The majority of service members who were referred for mental health treatment, got that treatment,” Hoge said. “We’re trying to encourage soldiers to come in early because we know that earlier treatment of mental health problems is the best way to prevent the long-term consequences that we’ve seen from past wars.

“The findings have important implications for estimating the level of mental health services that may be needed,” Hoge added.