Suicides among U.S. military soldiers have shot-up this year, with an average of one suicide a day -- the fastest so far during the nation's decades-long span of war.

The 154 suicides for active-duty troops in the first 155 of the year actually overlaps the number of U.S. forces killed in action in Afghanistan by approximately 50 percent, according to Pentagon statistics obtained by the Associated Press.

The increase in suicides comes after the military suicide rate leveled off in 2010-11.

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 soldiers who never deployed commit a substantial proportion of Army suicides.

The 154 suicides through June 3 this year accounted for 24 more than during the same period last year-an 18 percent increase-according to the Associated Press analysis of Pentagon figures.

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.

The Pentagon has said it is working to resolve these issues.