Two days after Sinha, a JPC member, wrote to him, Singh responded by saying that all "pertinent" documents related to 2G spectrum allocation of 2008 were available with the JPC.
"The decision as to what evidence should be sought and which individuals should be asked to appear before the JPC is a matter that needs to be decided internally by the JPC and its Chairman," the Prime Minister said in his letter to Sinha.
"You are aware that all pertinent records and documents available with the Government have already been placed at the disposal of the JPC," he told the BJP leader.
Sinha's letter to the Prime Minister had triggered a fresh war in JPC with its chairman P C Chacko yesterday rubbishing the demand as a "political stunt".
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Chacko said Sinha's letter to the Prime Minister directly asking him to appear before the JPC was against established norms.
The BJP leader had contended that Raja had levelled "serious allegations" against Singh and if he had nothing to hide, he should not hesitate to appear before the JPC.
Raja, who has repeatedly failed to persuade JPC to call him as witness, wrote to the committee last month saying the Prime Minister had been kept in the loop on 2G spectrum allocation.