Union Home Minister Rajnath Singh on Monday held a meeting to review Prime Minister Narendra Modi's security following recovery of a letter purportedly written by Maoists discussing plans to kill him.

Rajnath was joined by National Security Advisor Ajit Doval, Home Secretary Rajiv Gauba and Intelligence Bureau Director Rajiv Jain in the meeting.

The Ministry of Home Affairs (MHA) is already in possession of a report from Maharashtra Police regarding "certain communications among individuals having links to Maoist organisations containing references to targeting the prime minister," a senior MHA official said.

Rajnath asked officials to take all necessary measures in consultation with other agencies to suitably strengthen the security arrangement for the prime minister.

The Maharashtra Police last week told a court that they had seized a "letter" from the Delhi residence of one of the five people arrested last Wednesday for alleged "links" with the banned CPI (Maoist). The letter allegedly mentioned a plan to "assassinate" the prime minister in "another Rajiv Gandhi-type incident".

The letter had raised political heat with Opposition parties and activists questioning the genuineness of the letter. NCP chief Sharad Pawar said the threat letter "did not have any substance and was merely being used to garner people's sympathy" while the Congress called for a thorough probe but said the government or the BJP should not politicise it.

Questions were also raised about the authenticity of the letter, saying no one would discuss such plans through letters.

The BJP on Monday questioned the Opposition "insensitivity" over the life threat to Modi.

Senior BJP leader and HRD Minister Prakash Javadekar said the silence of some parties and some remarks, like the one of NCP chief Sharad Pawar, was not proper.

"Two Prime Ministers of India been brutally assassinated in the past. One would have thought that opposition parties, especially the Congress, would be sensitive about threats to the Prime Minister Modi's life. Comments by Pawar are also inappropriate," Javadekar told reporters.