The US military on Friday said the army private suspected of passing secret documents to WikiLeaks is being treated humanely in prison, despite accusations of harsh conditions.

Held at a military brig at the Quantico Marine base, Bradley Manning has been placed under a maximum security regimen because authorities see him as posing a risk to national security, said prison spokesman First Lieutenant Brian Villiard.

"Maximum custody detainees" include "those whose escape would cause concern of a threat to life, property or national security," Villiard told media.

"What I will tell you is that he is not treated any differently than any other maximum confinement detainee," he said.

Under the stricter security rules, Manning is allowed out of his cell for only one hour a day for exercise outside or at an indoor gym, prompting allegations from some commentators that he is enduring abuse.

The solitary confinement "constitute cruel and inhumane treatment and, by the standards of many nations, even torture," Glenn Greenwald, a lawyer and author, wrote on Salon.com.

The "accused leaker is subjected to detention conditions likely to create long-term psychological injuries," even though Manning has not been convicted of any crime, said Greenwald, who appeared on television on Friday.

The accusations came the same day that WikiLeaks founder Julian Assange was freed on bail in Britain, as he fights extradition to Sweden on charges of sexual assault.

But the military defended the detention conditions for Manning, saying other inmates placed in the highest security category were subject to the same rules.

The inmates at the brig "are treated with firmness, fairness, dignity and compassion," Villiard said.

But he added: "It's no Shangri-la."

Manning has access to newspapers, is within speaking range of other inmates in his wing, is permitted visitors and chooses from the same food menu as his fellow prisoners.