When contacted, Thomas told PTI here that the decision to appoint him and Singh as observers for the Rajya Sabha polls in Karnataka was taken by Congress President Sonia Gandhi.
Both Singh and Thomas will leave for Bengaluru from New Delhi tomorrow evening.
The decision came a day after Congress approached the Election Commission pleading against countermanding the election to four Rajya Sabha seats from the state in the backdrop of "sting operations" purportedly showing MLAs negotiating a money deal in exchange for their votes.
Later talking to reporters, Singh had dismissed suggestions that the matter was "serious" and warranted cancellation of the polls.
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Noting that Jharkhand had witnessed cancellation of Rajya Sabha polls in March 2012 after a candidate was caught with huge cash in his vehicle, Singh said that nothing of this sort has happened in Karnataka.
A political slugfest broke out in Karnataka over the "sting operations".
The Commission had sought a factual report from the Chief Electoral Officer of Karnataka.
Five candidates are in the fray for four seats in the RS polls.