According to Sangma, Mukherjee was chairman of the Kolkata-based Indian Statistical Institute (ISI).

The ISI quickly denied the allegation, saying Mukherjee quit June 20, eight days before he filed his nomination as the United Progressive Alliance (UPA) candidate.

"He had resigned on June 20. The confusion has been created because this was not updated on the institute's website," the ISI official told IANS from Kolkata.

The Congress supported the ISI's view.

"According to my information, he has resigned," Congress spokesperson Rashid Alvi told IANS.

Biju Janata Dal (BJD) leader Bhartruhari Mahtab, who is Sangma's poll agent, however, questioned if the institute had accepted the resignation.

"They should give out the date when they accepted the resignation. Only giving resignation means nothing," Mahtab told IANS.

He also said that Parliamentary Affairs Minister Pawan Kumar Bansal, who is the election agent of the former finance minister, has sought more time for the reply.

"They have sought time to give a reply. If all is well, why have they sought more time to give a reply," Mahtab said.

The BJP said it will take up the matter with the Election Commission of India.

"We will appeal all the records in this connection with ISI should be seized and looked into," BJP leader Ravi Shankar Prasad told reporters.

In a complaint to Rajya Sabha Secretary General V. K. Agnihotri, who is the returning officer for the presidential election, Sangma's lawyer Satpal Jain demanded that Mukherjee's candidature be cancelled as he is still the ISI chairman.

Bansal termed the complaint as "factually incorrect" and told reporters that Mukherjee will give a written reply to the returning officer by 3 p.m. Tuesday.

Sangma is backed by the Bharatiya Janata Party (BJP), Tamil Nadu Chief Minister and AIADMK leader J. Jayalalithaa and Odisha Chief Minister and BJD leader Naveen Patnaik.

In Bhubaneswar, Patnaik had also accused Mukherjee of buying support of parties by doling out large sums of money to selective states during his tenure as finance minister.

"Pranab Mukherjee as finance minister of India had doled out huge sum of money... lakhs of crores... to certain states like Bihar, Bengal and UP," Patnaik told reporters Sunday night after returning from New Delhi.

Meanwhile, official sources said the scrutiny of nomination papers, which started July 2, will continue July 3.

The last date of withdrawal of candidature is July 4. The election is slated for July 19 and counting is on July 22.