His comments come as the opposition is demanding that he be interrogated about his government's assignation of two coal blocks in Odisha to a firm owned by industrialist Kumar Mangalam Birla.
The entrepreneur and the government's former coal secretary PC Parakh have been accused by the CBI of criminal conspiracy in the deal.
The CBI has not named the Prime Minister in its First Information Report or FIR, but has said the contract was endorsed by "the competent authority," which is being interpreted as a reference to Dr Manmohan Singh since he held direct charge of the Coal Ministry at the time.
In a statement released days ago, Dr Singh's office said that the deal was "entirely appropriate."
The national auditor said in 2012 that the lack of a transparent bidding process for mining rights cost the country 1.86 lakh crores.
The CBI has requested the Prime Minister's Office to hand over all documents relevant to Mr Birla's coal block deal. Sources in the agency say once they have reviewed the files, they will decide whether Dr Singh needs to be questioned.
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