Singh died of a massive heart attack at a private hospital in Bengaluru this morning, doctors said.
"Saddened by the demise of former Karnataka CM Shri N. Dharam Singh. My thoughts are with his family & supporters in this sad hour," the prime minister tweeted.
"Shri N. Dharam Singh had rich experience in Karnataka & national politics. His dedicated service towards society will be remembered," Modi added.
Eighty-year-old Singh, ailing for the last few months, fainted at his home and was rushed to M S Ramaiah hospital where doctors declared him dead about 40 minutes later.
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