The findings came as President Barack Obama weighs whether to send additional forces to Afghanistan and amid a renewed focus on the mental fitness of troops after a deadly shooting rampage last week by an army psychiatrist at Fort Hood in Texas.
Only 5.7 percent of soldiers surveyed in Afghanistan rated morale for their units as high or very high, compared to 10.2 percent in 2007, according to the assessment.
But soldiers were more positive about their personal morale, with 17.6 percent saying their own morale was high or very high compared to 15.4 percent two years ago.
Soldiers in Afghanistan who had gone through three or more deployments were "significantly more likely to meet the criteria for a psychological problem" than those on their first and second deployment, the report said.
Among troops facing three or more deployments, 31 percent were suffering from mental health problems compared to 18.1 percent of soldiers on their second deployment and 13.6 percent on their first combat tour, it said.
And marital problems were dramatically higher among soldiers with three or more combat tours, with 30.8 percent experiencing marital crises compared to 14.3 percent for those on their first deployment.
The team that carried out the surveys recommended the army deploy more mental health specialists to Afghanistan -- where soldiers reported increasing problems getting access to care -- to reach a ratio of one provider for every 700 soldiers.
Currently, the ratio is one to 1,123 but officers said more than 60 mental health specialists were due to deploy, ensuring the army would meet the goal of one per 700 soldiers by the end of the year.
"We are making adjustments right now in the request for forces to come within the one to 700 ratio," Lieutenant General Eric Schoomaker, the army surgeon general, told reporters in a teleconference.
The rugged Afghan terrain, difficult weather and the dispersal of troops in smaller outposts required more mental health teams to reach soldiers who needed help, he said.
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Image: AFP/Mandel Ngan.