'Serious problem'

Recent congressonal declassified documents have shown that Rice approved the CIA plan to waterboard detainees - applying the technique of simulated drowning on them.

Hillary Mann Leverett, a former US diplomat, told Al Jazeera: "Either way this is a serious problem for her.

"In the documents ... that have been declassified, it is her name that is there - either authorising or, as she puts it, conveying the authorisation.

"But conveying the authorisation from whom? She only worked for one person," Leverett said.

Legal immunity

Mark Taylor, an international law expert, said paper trails and approval processes showed there was "high [level] approval given for those interrogations". 

He said prosecuting those responsible would "depend on whether the attorney general is willing to pursue the case".

Barack Obama, the US president, has said waterboarding is torture but former Bush administration officals have maintained it was not and that use of the technique prevented attacks on the US.

The Obama administration has left the door open to prosecute those who authorised torture, but has said it will not charge people who carried out orders to use torture.

Obama recently assured CIA operatives that they would be granted legal immunity with respect to waterboarding.