FORT MEADE, Md. – Bradley Manning, the Army private arrested in the biggest leak of classified material in U.S. history, pleaded guilty Thursday to charges that could send him to prison for 20 years, saying he was trying to expose the American military's "bloodlust" and disregard for human life in Iraq and Afghanistan.

Military prosecutors said they plan to move forward with a court-martial on 12 remaining charges against him, including aiding the enemy, which carries a potential life sentence.

"I began to become depressed at the situation we found ourselves mired in year after year. In attempting counterinsurgency operations, we became obsessed with capturing and killing human targets on lists," the 25-year-old former intelligence analyst in Baghdad told a military judge.