WASHINGTON—Suicides are surging among America's troops, averaging nearly one a day this year -- the fastest pace in the nation's decade of war.

The 154 suicides for active-duty troops in the first 155 days of the year far outdistance the U.S. forces killed in action in Afghanistan -- about 50 percent more -- according to Pentagon statistics obtained by The Associated Press.

The numbers reflect a military burdened with wartime demands from Iraq and Afghanistan that have taken a greater toll than foreseen a decade ago. The military also is struggling with increased sexual assaults, alcohol abuse, domestic violence and other misbehavior.

Because suicides had leveled off in 2010 and 2011, this year's upswing has caught some officials by surprise.

The reasons for the increase are not fully understood. Among explanations, studies have pointed to combat exposure, post-traumatic stress, misuse of prescription medications and personal financial problems. Army data suggest soldiers with multiple combat tours are at greater risk of committing suicide, although a substantial proportion of Army suicides are committed by soldiers who never deployed.

The unpopular war in Afghanistan is winding down with the last combat troops scheduled to leave at the end of 2014. But this year has seen record numbers of soldiers being killed by Afghan troops, and there also have been several scandals involving U.S. troop misconduct.

The 2012 active-duty suicide total of 154 through June 3 compares to 130 in the same period last year, an 18 percent increase. And it's more than the 136.2 suicides that the Pentagon had projected for this period based on the trend from 2001-2011. This year's January-May total is up 25 percent from two years ago, and it is 16 percent ahead of the pace for 2009, which ended with the highest yearly total thus far.

Suicide totals have exceeded U.S. combat deaths in Afghanistan in earlier periods, including for the full years 2008 and 2009.

The suicide pattern varies over the course of a year, but in each of the past five years the trend through May was a reliable predictor for the full year, according to a chart based on figures provided by the Armed Forces Medical Examiner.

The numbers are rising among the 1.4 million active-duty military personnel despite years of effort to encourage troops to seek help with mental health problems. Many in the military believe that going for help is seen as a sign of weakness and thus a potential threat to advancement.

Kim Ruocco, widow of Marine Maj. John Ruocco, a helicopter pilot who hanged himself in 2005 between Iraq deployments, said he was unable to bring himself to go for help.