The US soldier accused of leaking large numbers of secret documents to Wikileaks has pleaded guilty to 10 of the 22 charges against him.
In court, Bradley Manning read a statement explaining his actions, saying he did not believe the leaks would harm the US
But Pfc Bradley Manning, 25, denied the most serious charge against him, aiding the enemy, and may still be prosecuted.
A military judge later accepted the guilty pleas, with which he could face up to 20 years in prison.
On Thursday, Pfc Manning told a court he divulged the documents to spark public debate about US actions.
At the military court in Fort Meade, Maryland, Judge Col Denise Lind accepted Pfc Manning's guilty pleas, but prosecutors can still pursue a trial on the remaining 12 charges, including aiding the enemy.
That charge carries a potential life sentence.
Pfc Manning read out a statement to the court on Thursday saying he believed the leaked material would stimulate public discussion.
"I believed that if the general public, especially the American public, had access to the information... this could spark a domestic debate on the role of the military and our foreign policy in general," Pfc Manning told the court.
He said he would plead guilty to sending the documents to Wikileaks in violation of military regulations but would not plead guilty to a violation of federal espionage laws.
"I thought these cables were a prime example of the need for a more open diplomacy," said Pfc Manning, who addressed the court in uniform.
"I believed that these cables would not damage the US. However, I believed these cables would be embarrassing."
The soldier also mentioned his shock at discovering a video of an aerial combat mission in Iraq in which two employees from the Reuters news agency were killed.
"The most alarming aspect of the video to me was the seemingly delightful bloodlust the aerial weapons team happened to have," he said, comparing the troops to children "torturing ants with a magnifying glass".
Pfc Manning is accused of sending thousands of battlefield reports from both Afghanistan and Iraq, 250,000 diplomatic cables, and other classified material to the Wikileaks website in 2009 and 2010 while working as an Army intelligence analyst in Baghdad.
It is considered the largest-ever leak of secret US government documents.
The Obama administration has said the leaks threatened valuable military and diplomatic sources.
Supporters, who consider him a whistleblower who exposed war crimes and helped trigger the upheavals of the Arab Spring, held events on Saturday to mark his 1,000th day of detention.
The judge has ruled any eventual prison sentence should be reduced by 112 days due to his treatment at a maximum security facility in Virginia earlier in the case.
He has since been transferred to a medium-security jail.