Thiruvananthapuram: The Kerala Police has intensified its probe into a death threat against former ISRO chairman G Madhavan Nair, warning him not to support Prime Minister Narendra Modi, an intelligence official said here on Friday.

Speaking to IANS, the official, on condition of anonymity, said the threat came in a letter two days ago.

"The death threat that came in a letter, mentions the name of the Jaish-e- Mohammed terror group. It has now been sent for a high-profile forensic examination and the test results are awaited. The police have already registered a case and detailed investigations are going on by multiple probe teams of the Kerala Police," he said.

The 75-year-old Nair, who resides in the heart of the state capital, retired as chairman of the Indian Space Research Organisation in 2009 and is a Padma Bhushan and Padma Vibhushan awardee.

He played a crucial role in the design and development of the cryogenic engine for the Geosynchronous Satellite Launch Vehicle (GSLV).

Last year, Nair joined the Bharatiya Janata Party.