Ex-US state department spokesman PJ Crowley, who quit after criticising the treatment of the man accused of leaking secret cables to Wikileaks, has told the BBC he has no regrets.
Mr Crowley told the HARDtalk programme that the treatment of Bradley Manning was undermining "a very legitimate" effort to prosecute him.
Pte Manning has been held in shackles in solitary confinement.
Mr Crowley left the department after calling his treatment "stupid".
"I thought the treatment of Bradley Manning was undermining what I considered to be a very legitimate prosecution of an individual who has profoundly affected US national security," Mr Crowley said in his first public remarks since stepping down on 13 March.
He said he had not anticipated his criticism of another arm of the US government - the military - would spark such a controversy, and said it was appropriate for him to step down because his remarks had put President Barack Obama in a "difficult position".
"Quite honestly I didn't necessarily think the controversy would go as far as it did but I don't regret saying what I said," Mr Crowley said.
Mr Crowley, a former Air Force officer and national security aide to former President Bill Clinton, declined to say whether he had been asked to resign.
Pte Manning is being held at the US Marine Corps base in Quantico in the US state of Virginia, pending trial on 34 charges related to the leaking of 720,000 secret US military and diplomatic documents to the Wikileaks website.
Supporters say he has been held under harsh conditions, confined to a spartan cell for for 23 hours a day without a pillow, sheets, and personal possessions, and forced regularly to disrobe.
At a forum at the Massachusetts Institute of Technology this month, Mr Crowley was asked to comment on the matter.
"What is happening to Manning is ridiculous, counterproductive and stupid, and I don't know why the DoD [Department of Defence] is doing it," he said. "Nevertheless, Manning is in the right place."
Mr Crowley affirmed his remarks were on the record but later clarified the opinions were his own, not those of the state department.
"I'm a believer in something like strategic narratives," he told HARDtalk on Monday, "that the US, as an exceptional country in the world, has to be seen as practicing what we preach."