Veteran whistle-blower Daniel Ellsberg and a retired US Army colonel were among protestors arrested on Sunday outside the Quantico Marine Corps Base in Virginia, as hundreds gathered to protest at the treatment of WikiLeaks suspect Bradley Manning.
Manning, the 23-year-old Army private accused of passing hundreds of thousands of classified military and State Department documents to the whistle-blowing site, has been held in virtual isolation since his arrest last May, under conditions described by some commentators as 'torture'.
Reports indicate that Manning is woken every hour during the night, denied basic comforts such as sheets or a pillow, and has been forced to strip naked for long periods.
Last week, State Department spokesman PJ Crowley was forced to resign after calling Manning's treatement "ridiculous and counterproductive".
Local police made 34 arrests after protesters allegedly blocked a road intersection outside the base. Those arrested included former marine Ellsberg and retired US Army colonel Ann Wright.
Around 400 protesters, including many military veterans, had gathered to march outside the gates at Quantico, carrying placards with the slogan "Free Bradley Manning".
One veteran, Zach Choate, wearing the US purple heart medal given to servicemen killed or injured in conflict, described Manning as "an American war hero".
In an interview with news channel CNN, Ellsberg, the man who lifted the lid on US conduct during Vietnam war with the infamous 1971 'Pentagon Papers' leak, said:
"The president could change this treatment of him. He's been told by the Defense Department that it's appropriate... that's a terrible commentary on our standards. It means that they feel free to use illegal measures on someone in their custody."
Ellsberg said that former Hillary Clinton aide PJ Crowley had "acted honourably and boldly" by expressing his views on Manning's treatment.
David House, a friend of Manning's who has visited the soldier in jail, told CNN: "I think whistleblowing is a necessary part of any democracy... People must understand what's happening in our governments in order to make informed decisions."
Protesters later addressed US president Barack Obama and Defense Scretary Robert Gates in an open letter, also signed by celebrities including REM's Michael Stipe and actors Danny Glover and Viggo Mortensen.