By Medina Roshan

FORT MEADE, Md., Nov 29 (Reuters) - A U.S. Army private facing court-martial on suspicion of leaking secret documents to the WikiLeaks website testified on Thursday he was confined to a "cage" in the early days after his arrest in 2010, and thought he would die there.

Bradley Manning, in his first public comments since his arrest in Iraq, said his isolation quickly led to a breakdown, and his military captors eventually put him on suicide watch.

"My nights were my days and my days were my nights," Manning said. "It all blended together after a couple of days."

The low-ranking soldier Manning faces up to life in prison if convicted of charges he played a role in the massive leaking of secrets by WikiLeaks, which stunned governments around the world by publishing intelligence documents and diplomatic cables, mostly in 2010.

Manning's lawyers were working on a plea deal involving less serious charges that would result in a prison term of at least 16 years, one of his attorneys said.

His captors initially gave Manning little or no information about the charges against him as he was taken from Iraq to a U.S. detention facility in Kuwait, he said.

Manning said he was confined to a structure he called a "cage" of eight feet (2.43 metres) square inside a tent. He suffered a breakdown about a month after his May 2010 arrest, and guards later found a noose in the cage. Manning had made the noose but failed to recall he had done so because he was so disoriented, he said.

"I remember thinking I'm going to die stuck here in this cage," Manning said. "I thought I was going to die in that cage. That's what I saw - an animal cage."

Upon being transferred to Quantico, Virginia, in July of 2010, Manning was placed in solitary confinement for up to 23 hours a day, on suicide watch with a guard checking on him every few minutes. He was often noticed playing peek-a-boo in the mirror.

"The most entertaining thing in there was the mirror. I spent quite a lot of time with the mirror," Manning said. When asked why, he said, "Just sheer, complete, out-of-my-mind boredom."

The private's testimony, which was set to continue into Friday when he would be cross-examined, came on the third day of a hearing at Fort Meade, Maryland, to determine whether his case should proceed to a full court-martial.

In the absence of a plea deal, Manning's case could go to trial, where he faces possible life imprisonment if he is convicted of all the security breach charges against him.

LINKS TO WIKILEAKS

Charges include stealing records belonging to the United States and wrongfully causing them to be published on the Internet and aiding enemies of the United States, identified by prosecutors as al Qaeda in the Arabian Peninsula, an affiliate of the militant network founded by the late Osama bin Laden.

Prosecutors have alleged that Manning, without authorization while on intelligence duty, disclosed hundreds of thousands of U.S. diplomatic cables, military reports and video of a military helicopter attack in Iraq in which two Reuters journalists were killed.

WikiLeaks has never confirmed Manning was the source of any documents it released.

In pre-trial litigation, prosecutors have presented testimony legal experts say could be used to build a case Manning had been in email contact with Julian Assange, WikiLeaks' Australian-born founder.

Assange has spent nearly six months in the Ecuadorean Embassy in London, where he sought refuge to avoid extradition to Sweden for questioning in a sexual molestation case.

Assange and his supporters have said the Swedish case against him could be part of a secret plot to have him shipped for trial to the United States and either executed or imprisoned at the U.S. detention facility in Guantanamo Bay, Cuba.

U.S. officials have denied those assertions. But they have acknowledged a federal grand jury in Alexandria, Virginia, has been collecting evidence about WikiLeaks. U.S. officials have not ruled out criminal charges against Assange.

Earlier on Thursday, Assange played down reports that his health was declining after Ecuadorean officials said he was suffering from a chronic lung ailment.

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