The Pune Police has unearthed a letter that suggests plans to assassinate Prime Minister Narendra Modi.

The letter was unearthed while probing Maoists links to the January 1 Koregaon-Bhima caste violence in Maharashtra.

"We are thinking along the lines of another Rajiv Gandhi-type incident...It sounds suicidal and there is a good chance we might fail but we feel the party must deliberate over our proposal," the letter states.

The letter found in Rona Wilson's house in Delhi refers to the need to have Rs 8 crore to procure M-4 rifle and four lakh rounds, and also mentions "another Rajiv Gandhi-type incident".

Former prime minister and Congress president Rajiv Gandhi was killed by an LTTE suicide bomber while campaigning for the Lok Sabha elections at Sriperumbudur, Tamil Nadu, in May 1991.

This development follows the arrest of Surendra Gadling, general secretary of Indian Association of People’s Lawyers from Nagpur; Prof Shoma Sen, head of Department of English, Nagpur University; Sudhir Dhawale, editor of 'Vidrohi' from Mumbai; Rona Wilson, public relations secretary, Committee for the Release of Political Prisoners (CORPP), and Mahesh Raut, anti-displacement activist from Bharat Jan Andolan and former Fellow at Prime Minister’s Rural Development (PMRD) for Gadchiroli district.

They were arrested by the Pune Police on Tuesday in connection with the Koregaon-Bhima riots. They were produced before the court and later remanded to police custody till June 14.

The arrests and searches have been purportedly made under the FIR registered on January 8 at Vishram Baug Police Station in Pune with regard to organising the Elgar Parishad on December 31, 2017, by the Bhima-Koregaon Shaurya Din Prerna Abhiyan.

The FIR, originally registered under Section 505 (1)(b), 117 and 34 of the Indian Penal Code (IPC), was made a conspiracy case in March and now has had sections of the Unlawful Activities Prevention Act (UAPA) added to it.