The Pentagon said 349 active-duty troops killed themselves in 2012, up more than 15 percent from 2011 despite renewed efforts by the military to stem the suicide rate.
"This is an epidemic that cannot be ignored," said Senator Patty Murray, who championed legislation last year to improve suicide prevention efforts and mental health care for troops and veterans.
"As our newest generation of servicemembers and veterans face unprecedented challenges, today's news shows we must be doing more to ensure they are not slipping through the cracks."
The Army, as the largest service, counted the biggest number of suicides, with 182 soldiers killing themselves in 2012, according to preliminary figures. The Navy had 60 suicides, the Air Force had 59 and the Marines had 48.
The figures were first reported by the Associated Press.
The Pentagon pointed to steps to bolster suicide prevention efforts, including expanding a suicide prevention hotline. Still, Defense Secretary Leon Panetta last year acknowledged that the suicides were the most frustrating issue he had faced since taking over the Pentagon in 2011.
"Despite the increased efforts, the increased attention, the trends continue to move in a troubling and tragic direction," Panetta told at a joint Pentagon-Department of Veterans Affairs suicide prevention conference in June.
The suicide figures far surpassed the 237 U.S. troops killed in action last year in Afghanistan, as well as the 313 killed in support of the Afghan war more broadly -- a figure that includes deaths outside the country. It was the highest number of suicides since the United States went to war in Afghanistan in 2001.
The Department of Veterans Affairs estimates that, roughly, a veteran commits suicide once every 80 minutes in America, a trend that may be worsening.
Last year, Reuters reached out to every state in the United States to inquire about suicides among veterans. Data collected from 32 states showed an increase in suicides between 2005 to 2010