The father of Bradley Manning has criticised his son’s treatment in a military jail.

The US soldier, who is understood to be gay, is accused of leaking secret cables to WikiLeaks.

He is currently being held at a military base in Virginia, awaiting a court martial on charges of handing state secrets to an unauthorised party.

The soldier is being kept in solitary confinement and is on suicide watch, with guards checking on him every five minutes. He has also been forced to sleep naked.

A report by Amnesty International said he was spending “23 hours a day in a sparsely furnished solitary cell and [has been] deprived of a pillow, sheets, and personal possessions since July 2010″.

His father, Brian Manning, has not commented until now.

But in a television interview with Frontline, he said he was moved to comment by reports of his son’s treatment.

He said: “It’s shocking enough that I would come out of our silence as a family and say, ‘No, you’ve crossed a line. This is wrong’.”

Brian Manning, a former Navy intelligence specialist, said his son had “not gone to trial or been convicted of anything” and drew parallels between his treatment and that of prisoners at Guantanamo Bay.

Bradley Manning was reportedly disowned by his family after coming out as gay.

His father revealed he had “twisted his arm” to get him to join the Army.

He said: “He didn’t want to join. But he needed structure in his life, he was aimless. I knew in my own life that joining the navy was the only thing that gave me structure, and everything’s been fine since then.

On whether his son did leak the documents to WikiLeaks, he said: “I don’t know why he would do that, I really don’t.”

“Whoever released those documents, it was the wrong thing to do,” he said. “You just don’t go there.”

Last week, a US state department spokesman resigned after calling Bradley Manning’s treatment “stupid.”

PJ Crowley told an audience at the Massachusetts Institute of Technology: “What is happening to Manning is ridiculous, counterproductive and stupid, and I don’t know why the DoD [Department of Defense] is doing it. Nevertheless, Manning is in the right place.”