The opposition forced three adjournments before lunch over the issue, asking Coal Minister Sriprakash Jaiswal to recuse himself from replying and demanding that Prime Minister Manmohan Singh should make a statement.
They said "propriety" demands Jaiswal should abstain as the missing files reportedly relate to a beneficiary of coal block allocation who is linked to the Minister.
Jaiswal sought to mollify the opposition as he said he was ready to face any punishment if found guilty of the allegations.
"All efforts are being made to locate documents which are not readily available...My Ministry would leave no stone unturned in tracing and providing the documents sought by the CBI," he said, adding a total of 769 files and documents running into 1.5 lakh pages have been handed over to the investigating agency.
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Raising the issue earlier, Jaitley said there are media reports that one of the beneficiaries of the coal block allocation was some body with whom the Coal Minister was related.
"Propriety demands that the Minister should voluntarily not speak...It should be the Prime Minister who should speak," said Najma Heptulla (BJP), asking the Chair to give a ruling in this regard.