Pranab Mukherjee's remarks were seen to refer to current commissioners in the election body.

Former President Pranab Mukherjee on Tuesday expressed concern at allegations of EVM or vote machine tampering - described by him as tampering of voters' verdict -- and said the "onus of ensuring institutional integrity" lies with the Election Commission. "The safety and security of EVMs which are in the custody of the EC is the responsibility of the Commission," Pranab Mukherjee said in a statement.

A series of video clips have surfaced, which, opposition parties say, prove that EVMs (Electronic Voting Machines) are being tampered with or being transported in private cars in parts of Uttar Pradesh, Bihar, Punjab and Haryana.

"There can be no room for speculation that challenge the very basis of our democracy. People's mandate is sacrosanct and has to be above any iota of reasonable doubt," said the former president. "A firm believer in our institutions, it is my considered opinion that it is the 'workmen' who decide how the institutional 'tools' perform," he added.

On Monday, Mr Mukherjee had said at the release of a book by NDTV's Editorial Director Sonia Singh that "institutions are fine and these institutions are built over the years. I do believe only a bad workman quarrels with his tools. A good workman knows how to utilise these tools."

The remarks were seen to refer to current commissioners in the election body that has been under attack from the opposition over allegations of bias.

In videos that are being circulated just two days before counting of votes in the national election, EVMs are transported in open trucks.

One video said to be from the Chandauli Lok Sabha constituency in Uttar Pradesh shows EVMs being off-loaded and stacked in a room. The clip shows some people, apparently supporters of the Samajwadi Party, questioning it.

The Election Commission called the allegations of manipulation "baseless" and "frivolous".