A US soldier killed in Iraq returned home in Jackson, Michiga, Dec. 19, 2006 (AFP Photo)

The suicide rate among US soldiers deployed in Iraq increased in 2005 after falling the previous year, according to a study by the US Army published on Tuesday.

The study said 22 soldiers serving in Iraq and Kuwait in support of Operation Iraqi Freedom had committed suicide, compared to 12 in 2004 and 25 in 2003.

The suicide rate was 19.9 per 100,000 in 2005, substantially higher than the rate in 2004, of 10.5 per 100,000.

For the whole of the US Army, the suicide rate was 13.1 per 100,000 in 2005 and 11.0 per 100,000 in 2004, the study said.

The majority of the suicides involved "white, unmarried males under the age of thirty" who were enlisted soldiers of a junior rank. The cause of death in most cases was a gunshot wound.

"The study determined that leading suicide risks factors were relationship issues at home and in theater, followed by legal actions, problems with fellow soldiers and command and duty performance," Jerry Harben of the US Army Medical Command Public Affairs said in a statement.

The suicide figures were part of a study that looked at the mental health and morale of army soldiers deployed in Iraq.

Of some 1,800 soldiers polled in October and November, 13.6 percent had acute stress symptoms and 16.5 percent suffered a combination of depression, anxiety and acute stress. These figures were higher than recorded in 2004 but lower than 2003.

The army said that among soldiers serving in successive deployments, 18.4 percent reported acute stress compared to 12.5 percent in their first deployment.

Soldiers who returned to Iraq for several tours reported their families suffered more stress and did not have enough time between deployments.