Campaigners from Wales are travelling to London to protest over the alleged treatment of a US army private accuses of leaking confidential papers.
Bradley Manning, who attended secondary school in Pembrokeshire, faces scores of charges over the documents handed to the Wikileaks website.
But there has been mounting concern about the conditions he is being held in at a military prison.
Cynon Valley MP Ann Clwyd tabled a Commons' motion on the issue last week.
"I think it is a serious case," she told BBC Wales.
"He's being held in solitary confinement, he's kept in his cell for 23 hours a day, not allowed to exercise, he's stripped of all his clothes during the night, he is not permitted to sleep during the day.
"Organisations like Amnesty International have already put out several press releases saying that Manning is being subjected to cruel, inhuman and degrading treatment."
In her early day motion, Ms Clwyd calls on the UK government to raise the issue with US counterparts, and to ensure the soldier's "detention conditions are humane" at the US Quantico marine base.
She added: "While I consider myself a friend of the Americans, I think it ill becomes them to treat one of their own soldiers in this way before he has been convicted, before he has been tried."
The issue of Pte Manning's treatment has been raised with President Obama
He said he had received assurances that the terms of Pte Manning's confinement were "appropriate".
But rallies highlighting the alleged plight of Pte Manning are now being held across the US, Canada and Europe.
The 23-year-old's mother is Welsh and still lives in Pembrokeshire, where he grew up from 13 and 17.
He went to Tasker Milward school in Haverfordwest, where the now retired deputy head teacher, John Broughton remembers him as "a very pleasant lad".
"A bit of a loner, you might say, computer interested," recalled Mr Broughton.
"He wasn't into sport or anything like that - not academically gifted but very pleasant, and worked reasonably well.
"He was always very talkative to me and other teachers, and he seemed to get on well with people."
Mr Broughton said he was alarmed at the reports of Pt Manning's treatment.
"It's just a shame - it's more than a shame, it's a disgrace really that he is being treated like he is," he said.
"It really is fairly shameful that the British government isn't doing anything about one of its own citizens."
Despite his Welsh mother, it is understood that Pte Manning does not have a British passport, and has not asked for UK assistance.
But his connections have prompted some to organise buses to join a rally in London on Sunday against his detention.
One campaigner, Vicky Moller, from Newport in Pembrokeshire, said: "Whether he is innocent of what he is charged with I don't know, but he is an innocent personality.
"He is young, he is well motivated, and I know that sensory depravation like isolation is one of the cruellest things you can do to a person.
"When I realised there was a Welsh connection, I felt that Wales could do something about it."