The Government has been urged to intervene in the case of a soldier held in a US jail on suspicion of passing state secrets to WikiLeaks - on the grounds that he is part-British.

Bradley Manning, a private in the US Army, went to school in Haverfordwest, Wales, where his mother still lives.

He has been accused of passing hundreds of thousands of diplomatic cables to the whistleblowing website.

Amnesty International argued that his Welsh parentage meant that the British government should step in in the wake of reports about the harsh conditions of his detention.

The human rights charity's director Kate Allen said: "Bradley Manning's Welsh parentage means that the UK government should be demanding that the conditions of his detention are in line with international standards and that his 'maximum custody' status does not impair his ability to defend himself. We would also like to see Foreign Office officials visiting him just as they would any other British person detained overseas and potentially facing trial on very serious charges."

Clive Stafford Smith, director of human rights charity Reprieve, echoed Amnesty's call.

"I don't care whether he's British or not, human beings have rights wherever they are. (But) the fact that he is a British national does give the Government standing to be involved," he said.

But the Government said it could not comment on Pte Manning's nationality.

A Foreign Office spokeswoman said: "We can't release any information on an individual's nationality unless we have their consent."

Pte Manning has been praised by WikiLeaks founder Julian Assange as "an unparalleled hero".