The Press Trust of India quotes Balamurugan, the general secretary of People's Union for Civil Liberties in Tamil Nadu as saying , "The family members received information from Belgaum prison authorities that the mercy petitions of the four have been rejected by the President."
The President's refusal to commute their sentence to life comes just days after he rejected a mercy petition filed on behalf of Afzal Guru, who spent eight years on death row after he was convicted for his role in 2001's deadly attack on the Indian Parliament.
Guru, a Kashmiri Muslim, was hanged on Saturday and buried at Delhi's Tihar Jail, provoking tension in Kashmir, where many parts remain under curfew.
Gnanprakasham, Simon, Meesekar Madaiah and Bilavendran - the convicts whose petitions have been turned down today - are in a jail in Belgaum, Karnataka. They were earlier sentenced to life by the TADA court in Mysore. But the government moved the Supreme Court, which awarded them the death sentence in 2004.
Veerappan was killed in an encounter with the Tamil Nadu in October 2004.