When asked his reaction to a Pentagon report that up to 70 sexual assaults are reported each day in the military, a 35 percent increase since he took office, Obama replied, "We have to do everything we can to root this out."
He called sexual assault "an outrage."
"And if it's happening inside our military, then whoever carries it out is betraying the uniform that they're wearing," he said when the subject was brought up at a joint White House news conference with South Korean President Park Geun-hye. "And they may consider themselves patriots, but when you engage in this kind of behavior that's not patriotic -- it's a crime."
Obama said his administration -- starting with his first defense secretary, Leon Panetta, and continuing with current secretary Chuck Hagel -- has been trying to create a structure with accurate reporting, accountability and transparency.
Obama said he spoke with Hagel Tuesday, "indicating to him that we're going to have to not just step up our game, we have to exponentially step up our game, to go at this thing hard."
"And for those who are in uniform who have experienced sexual assault, I want them to hear directly from their commander in chief that I've got their backs. I will support them," Obama said. "And we're not going to tolerate this stuff and there will be accountability.
"And anybody in the military who has knowledge of this stuff should understand this is not who we are. This is not what the U.S. military is about. And it dishonors the vast majority of men and women in uniform who carry out their responsibilities and obligations with honor and dignity and incredible courage every single day.
"So I don't want just more speeches or awareness programs or training but, ultimately, folks look the other way. If we find out somebody is engaging in this stuff, they've got to be held accountable -- prosecuted, stripped of their positions, court-martialed, fired, dishonorably discharged. Period. It's not acceptable.
The issue of sexual assault in the military drew renewed interest this week with the arrest of the U.S. Air Force officer in charge of sexual assault prevention.
Lt. Col. Jeffrey Krusinski, 41, was arrested Sunday in Arlington, Va., after he allegedly grabbed a woman's breasts and buttocks.
The Air Force has been hard-hit by a scandal in which more than 30 instructors have been charged with sexually abusing trainees at the entry-level training facility at Lackland Air Force Base in Texas.
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