We have not foreclosed charging other crimes against this individual should other evidence be developed or other evidence be made available

Richard Ashcroft

"Both in writing and orally he indicated that he wanted to make statements absent an attorney and that's a right we respect in America," Mr Ashcroft said.

Mr Walker is being tried in a civilian court on charges of conspiring to kill American citizens abroad and aiding Osama Bin Laden's al-Qaeda terror network.

The case of the 20-year-old Californian is being heard by the US District Court in Alexandria, Virginia, following a decision by US President George W Bush that only foreign nationals - not US citizens - will be sent to military tribunals.

Death penalty

Mr Ashcroft said that the charges were based mostly on statements voluntarily made by Mr Walker, who goes by his mother's maiden name.

Ashcroft said Walker refused counsel

If found guilty, Mr Walker could face life imprisonment, although the charges do not carry the death penalty.

But Mr Ashcroft said the charges could be increased as and when more evidence emerges.

"We have not foreclosed charging other crimes against this individual should other evidence be developed or other evidence be made available," he said.

Access denied

A lawyer hired by Mr Walker's family has complained that the accused has been denied access to an attorney.

"Despite repeated attempts by his family and his counsel to see him, John has not been given access to a lawyer," George Harris has complained.

"To the best of our knowledge, he has not even been informed that his parents have retained lawyers who are working on his behalf."

Charges against Mr Walker

Conspiracy to kill Americans overseas Supporting foreign terrorist organisations Transacting with the Taleban

Mr Walker was flown back to the US on 23 January after being held on the amphibious attack ship USS Bataan in the Arabian Sea, where he was recovering from his wounds.

He was taken into custody by US forces in November following a bloody prison uprising in Mazar-e-Sharif in November, in which an agent of the US Central Intelligence Agency was killed.