"I received info that BJP spokespersons Narasimha Rao and Amit Malviya accused me of being an ISI mole. If that is the case then Prime Minister Narendra Modi and Amit Shah are incompetent, why have not I been arrested? I will send both of them (Rao and Malviya) defamation notice," Singh said while addressing reporters.
Earlier, BJP leader Rao said that there is a "connection emerging between Congress' idea of Hindu terror and LeT and ISI's 26/11 strategy".
"We can see a connection emerging between Congress' idea of Hindu terror and LeT and ISI's 26/11 strategy. Was someone from India helping ISI as a handler to give terrorists Hindu identity? Was Digvijaya Singh working as a handler? Congress should answer this," he said.
The row over 'Hindu terror' has heated up again after ex-Mumbai Police Commissioner Rakesh Maria's book on 26/11 attacks.
Several sensational revelations have come in the high-profile book "Let Me Say It Now", released on Monday.
According to Maria, the LeT wanted him to be killed as a Bengaluru resident "Samir Dinesh Chaudhari", with a red thread tied around his wrist to portray the attack as a case of "Hindu Terror". However, that plan did not work out and the police nabbed Ajmal Amir Kasab, who was from Faridkot in Pakistan.
(with inputs from agencies)