He, however, stressed that the party would not bring a no-trust motion against the UPA government.
"The irregularities in allocation of coal blocks are part of the biggest-ever scam in the Independent India. BJP wants all the (coal block) allocations scrapped. We want that the prime minister resign on moral grounds," Singh told reporters here.
On allegations that BJP was holding Parliament to ransom over the issue, the former BJP president said, "In fact, the Congress-led UPA government at Centre has not done anything to ensure smooth functioning of the House".
Singh said the Congress was trying to "muzzle" the voice of constitutional bodies like the Comptroller and Auditor General (CAG) with the prime minister rejecting its findings on presumptive loss.
"Now, after the scam is exposed and BJP firming up its stand, Congress president Sonia Gandhi is asking her party to be aggressive. We want that prime minister should first resign from his post and a probe be conducted. Congress can reinstate him later if it wants so," Singh said.
He said that BJP would not bring a no-confidence motion against UPA government but wants all the coal block allocations made so far cancelled.
On allegations of irregularities in allocation of coal blocks in BJP-ruled Chhattisgarh, Singh said, "The state government followed due procedure in allotting the blocks and the entire process is transparent".