Campaigners call for the US soldier, whose mother is Welsh, to get consular access in the military prison where he is held

Campaigners on behalf of Bradley Manning, the US soldier accused of leaking classified cables to WikiLeaks, have welcomed assurances that the British government will restate its "concerns" to Washington over the soldier's treatment.

Manning, whose mother is Welsh, is being held in a military prison in Virginia, after being arrested in May 2010 on suspicion of leaking data including 250,000 diplomatic cables to the site.

His supporters argue that the conditions of his imprisonment – he is held in solitary confinement, stripped of his clothes every night and subjected to continual checks because he is deemed a suicide risk – are punitive and unduly harsh. The UN has launched an inquiry into whether his conditions amount to torture.

In a parliamentary debate late on Monday, the Foreign Office minister Henry Bellingham said staff at the British embassy in Washington had expressed concerns to the state department on 29 March about the treatment of Manning, who has not been tried or convicted. In response to the debate, he said, "we will instruct our officials at our embassy in Washington again to report our concerns to officials in the state department".

While acknowledging that Manning's lawyer has stated that he does not hold a British passport or consider himself to be British, the minister stressed that the soldier "is British by descent" despite being born in the US, thanks to his mother's nationality.

Naomi Colvin, from the UK Friends of Bradley Manning, welcomed the sympathetic approach of British ministers, adding: "We want Bradley to be given consular access. The British government should now support his family here in Wales, and somebody from the embassy should be visiting Bradley to report back."

The question of the 23-year-old soldier's conditions of detention was becoming a "strongly-felt issue" in Wales, said Colvin, "and Welsh nationalists in Plaid Cymru are keen to take this on".

Manning's father Brian, now divorced from his mother, met and married her when he was himself in the US military and stationed at Brawdy, near Haverfordwest. Manning was born in Oklahoma but spent some of his teenage years in Wales.

The case was raised in parliament by the Labour MP Ann Clwyd, who chairs the all-party parliamentary group on human rights. She said Manning's treatment was "cruel and unnecessary and we should be saying so". In response, Bellingham acknowledged that the US president, Barack Obama, had received assurances from the US military that Manning's treatment was "appropriate" and met "basic standards", but restated the government's commitment to "a foreign policy that will always have support for human rights ... at its irreducible core."

"As far as Her Majesty's government are concerned, the conditions in which an individual is detained must meet international standards," he said. "Conditions that fail to meet this standard may amount to cruel, inhuman or degrading treatment or punishment. This is particularly important for an individual in pre-trial detention."