Two of WikiLeaks suspect Bradley Manning's former prison guards have denied abusing him in custody, and described an incident where the US Army private suddenly burst into tears.

Manning, 24, is accused of providing Internet site WikiLeaks with hundreds of thousands of US diplomatic cables and classified war logs from Afghanistan and Iraq while based in Baghdad as a military intelligence analyst in 2009 and 2010.

If convicted, he could face life in prison.

The soldier's defense team argues that the case should be dismissed because of unduly harsh treatment he received in custody.

But on the fifth day of a pre-trial hearing at Fort Meade military base near the US capital, the prosecution maintained the military acted appropriately, taking evidence by telephone from his former guards.

Joshua Tankersly and Jonathan Cline recounted Saturday how when they were tasked with escorting Manning to a fitness room at Quantico brig on January 18, 2011, the detainee broke down under their close watch.

For hours the day before, dozens of demonstrators had blocked access to Quantico, in protest against the conditions of Manning's detention, which a UN rapporteur on torture has concluded amounted to cruel and inhumane treatment.

The guards described what happened when they attempted to put restraints on Manning in the exercise room.

"Detainee Manning was instructed to spread his feet" while they shackled his hands, and then "turn around, while we put the belt, and kneel while we put the legs restraints," Cline said, noting that the soldier had to be "corrected" because he was "moving his hands when we put on his restraints.

Tankersly said that when "we put him in restraints, he did not respond in a correct manner," noting that he twice told Manning to "stop moving."

When they took off the restraints, he began moving again.

"He fell down on his butt. We tried to catch him, he went hiding behind a weight machine and he began to cry," Cline said.

"It happened really fast," the former guard said, adding that he did not understand why he was subsequently suspended for having "intimidated" Manning.

Asked by Manning's civilian defense attorney David Coombs, neither guard remembered hearing Manning say "I'm sorry" as he cried. Nor did either remember if Manning was treated differently that day, following the demonstration.

But Cline admitted that prison staff were "annoyed" because as a result of the protests in front of the main gate, the staff needed to go through a different gate to go home.

Cline, who lived on the base and did not need to leave except to go grocery shopping, told Judge Denise Lind that he did not have any "personal anger" toward Manning after the protest.

The two guards also testified that Manning had always been "respectful" and "compliant," noting "he was like an average detainee," and that other than during this incident he never tried to escape, attack anyone or hurt himself.

"I spoke to him basically like to a normal human being. They're in the facility, that's their punishment. They don't need to be screamed at or yelled at," Cline said.

But Tankersly admitted Manning was allotted only a "20 minute sunshine call" each day, and if he used it, the time was deducted from one hour of authorized exercise time -- which was the only time he was allowed to leave his cell.

Marine Corps Gunnery Sergeant William Fuller, a supervisor, at Quantico said that after the gym incident Manning was "shaken pretty bad."

"He looked scared to me, he wasn't smiley," Fuller told the court. "He had a hard time breathing, kind of... panicking, he kept apologizing, I didn't figure out why he was sorry. I think he was frustrated with the staff in some way."

But Fuller said the measures taken with Manning were "not punitive, it's protection for the detainee."

"I considered him as suicidal," Fuller said of Manning, who is due to go on trial in February next year.

During his appearance Thursday, Manning recalled his first days in a tiny cell at a US military base in Kuwait in the summer of 2010, saying he thought he would never leave that cell alive.

"I thought I was going to die in that cage," he said. "And that's how I saw it, as an animal cage."