The Bush administration on Friday denied that a letter purportedly written by Senator Thomas Graham to a former US envoy in India in 1995 about a mole in the PMO was part of official correspondence.
It also said that no judgement about its authenticity could be made.
"One, we can't verify that this correspondence is authentic. Two, the two individuals between whom this alleged correspondence took place were at that time working in private non-governmental organisations. They weren't employed by the US government," US State Department spokesman Sean McCormack said at a briefing.
BJP leader Jaswant Singh had claimed that Graham had written a letter to former Ambassador Harry Barnes about a spy in then Prime Minister PV Narasimha Rao's office, who leaked nuclear secrets to the US.