Asserting that the Prime Minister must take moral, political and Constitutional accountability for all the scams that have taken place during his regime, senior Bharatiya Janata Party (BJP) leader Ravi Shankar Prasad on Saturday reiterated that Manmohan Singh should step down from his post and a fair probe must be conducted into the coal blocks allocation.

Prasad said it is the BJP's constitutional obligation as the principal opposition to ask questions from the Prime Minister and seek his accountability.

"If the people have elected you to govern the country, they have also given us the responsibility to become custodial of their interest and we shall continue to ask questions," said Prasad.

"Whether you call it 'Tu Tu Main Main' or seek solace about your silence by reciting certain Urdu couplet. Manmohan Singh we have a very straight question to ask from you, 'Why is it that some of the biggest shameful scandals and instances of corruption have taken place since Independence when you have been the Prime Minister?' The Commonwealth scam, the 2G scam, the Adarsh scam, the Airport land scam, now the coal blocks scam. We are seeking your moral, political and Constitutional accountability," he added.

Asserting that public interest was sacrificed and that the CBI has found many irregularities even in the preliminary investigation, Prasad said: "Is it not a fact that now it is reverent that under the pressure of your ministerial colleague, you as the Prime Minister also holding the Coal Ministry in-charge, was allocating coal blocks to their kith and kins?"

"Even on that basis, we are seeking your accountability, why different standards were used. If Raja as the Telecom Minister and Dayanidhi Maran were forced to resign in the wake of CBI investigations, why should you remain in office when the CBI investigation is on," he added.

Prasad demanded that the coal blocks allocation must be cancelled.

"The PM must resign and there must be a fair probe. That demand remains relevant and the more the Prime Minister opposes this, the more he is going to create a cloud over himself," he said.

The Prime Minister had earlier on Monday rejected the CAG's observations as 'misleading' and 'flawed', and blamed the opposition parties for thwarting the efforts of his government to bring a policy of competitive bidding.

Manmohan Singh, who spoke both inside Parliament as well as outside, took 'full responsibility' for the decisions taken by the Coal Ministry whose charge he directly held for some time and asserted that at 'any allegation of impropriety is without any basis and unsupported by facts'.

Singh, who is facing sharp criticism from the opposition over the CAG report on coal block allocations, also urged the BJP to debate the issue in Parliament and not disrupt proceedings.

The BJP has held the Prime Minister, who then held direct charge of the coal ministry, responsible for what has been estimated as a notional loss of Rs 1.86 lakh crores by the CAG in coal block allocations, and demanded his resignation.

The CAG report on coal block allocations states that nearly 150 coalfields were allotted to private and state-run firms without transparency and objectivity between 2005 and 2009.