Saying that it will be the "last nail in the coffin of Congress", BJP also hoped that Singh would now reveal what pressure he was under when coal blocks were "arbitrarily" allocated by the previous UPA government.
"Today's march is a 'Congress-bachao' march. Congress president Sonia Gandhi led it to save herself. A scared and worried Congress party is standing at (Singh's) door out of fear that the truth will be out now.
"What was the pressure on former PM Singh. People of the country will expect that at least now he will come out with the truth as to under whose pressure he was functioning," he said.
Sharma said that if only the Congress chief had extended her support to Singh in 2004, the party would not have suffered such "bure din" (bad days) as it is facing today.
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Several of Singh's former Cabinet colleagues, P Chidambaram, Anand Sharma, Ambika Soni and Veerappa Moily joined Gandhi for the march.
Congress leaders have also attacked the government over the issue, accusing it of maintaining a "studied silence" after CBI had told the court that there was no criminality involved in the allocation of Talabira coal block II to Aditya Birla group company Hindalco in Odisha in 2005, when Singh was also holding the coal portfolio.