Karnataka Congress president Dinesh Gundu Rao on Monday tendered his resignation to the party chief Sonia Gandhi, after the party suffered a massive defeat in the by-elections.

"Taking moral responsibility, I am resigning as the Karnataka Pradesh Congress Committee president," said Rao at the Congress office.

Rao said that the Congress thought people will not favour the defectors, yet the BJP won.

"Operation Kamala has been ratified by the people," said Rao, describing the way BJP attracted and fielded the disqualified Congress lawmakers.

The BJP had fielded 11 Congress and 3 JD-S defectors to wrest the seats from the opposition parties.

Rao said he will meet Congress president and submit a detailed report about the party's rout in the bypolls.

Earlier, following a humiliating defeat in the by-elections, Siddaramaiah also resigned as the leader of opposition in state Assembly.