The chief minister of India's southern state of Tamil Nadu is sticking to his controversial statement questioning the existence of Hindu God Ram.
Mr Karunanidhi refuses to budge from his stand
M Karunanidhi also said there was no proof that Lord Ram had constructed a bridge where a new shipping canal is planned between India and Sri Lanka.
Hard-line Hindu groups say the chief minister's statement is blasphemous.
On Tuesday Hindu activists angered by the comments set fire to a Tamil Nadu bus, killing two people, police said.
Enraged Hindu hardliners in the city of Bangalore, in neighbouring Karnataka state, also attacked the home of Mr Karunanidhi's daughter, Selvi.
Hindu scripture says the area between India and Sri Lanka - now known as Adam's Bridge - was built millions of years ago by Lord Ram, supported by an army of monkeys.
But scientists and archaeologists say Adam's Bridge, or Ram Setu, is a natural formation of sand and limestone. Hard-line Hindu groups say a proposed canal project between India and Sri Lanka will destroy the bridge.
They say Mr Karunanidhi's statement is blasphemous and have demanded an apology from him.
Hindu devotees believe the "bridge" was built by Lord Ram
"You tell me whether Ram lived. I had only stated that there was no person in the name of Lord Ram. What is wrong in that?" Mr Karunanidhi is reported to have told a TV channel.
On Saturday, addressing a public rally, Mr Karunanidhi had asked: "Who is this Ram? From which engineering college did he graduate?"
Angered by his statement, Hindu hard-line groups have demanded his dismissal and arrest.
Last Wednesday, the Archaeological Survey of India told the Supreme Court that religious texts were not evidence that Lord Ram ever existed.
Hard-line Hindu opponents of the government accused the administration of blasphemy and protesters held demonstrations in the area and in Delhi, Bhopal and on a number of key highways.
The next day the report was withdrawn.
In a damage control exercise, two directors of the Archaeological Survey of India were suspended and Culture Minister Ambika Soni offered to resign.
The government wants to build a canal to link the Palk Strait with the Gulf of Mannar by dredging a canal through the shallow sea.
The $560m Sethusamudram Ship Canal Project is expected to provide a continuous navigable sea route around the Indian peninsula and is expected to boost the economic and industrial development of the region.