WASHINGTON -- A new poll indicates the tough mission in Iraq is affecting the morale of American troops.

The survey by the military newspaper Stars and Stripes says one-third of U.S. troops surveyed in Iraq say their morale is low. Half say they're not likely to stay in the armed forces.

The paper says its August poll of about 2,000 troops isn't a scientific sampling, but the results are raising new worries that the long deployments and mission could prompt some military members to leave the military when it comes time to re-enlist.

The government-funded paper also says the top U.S. commander in Iraq is challenging the poll results. Lt. Gen. Ricardo Sanchez said, “there is no morale problem.”

Asked about their personal morale, 34 percent of the troops surveyed rated it as “low” or “very low,” 27 percent said it was “high” or “very high,” and the remainder called it “average.” Just over one-third say their mission hasn't been well defined.