A senior leader of the Democratic Youth Federation of India has lodged a complaint with Kerala police saying he received an anonymous letter threatening to “kill” chief minister Pinarayi Vijayan, a Left veteran known for his tough stand on communal politics.

Senior CPM leader P. Jayarajan, considered close to Vijayan, received a similar letter amid suspicions that two Muslim Right-wing groups were behind them — the Popular Front of India (PFI) and its political wing, the Social Democratic Party of India (SDPI).

The police have started a probe and are likely to form a special investigation team, sources said.

The threat to Vijayan came in the letter that A.A. Rahim, Kerala state secretary of the DYFI, received on Tuesday by regular post at the party office in Thiruvananthapuram.

“We have noted you and other Judases like that Pinarayi… we will kill your leader Pinarayi, just like buffalos are slaughtered,” the letter, handwritten in Malayalam, warned.

Vijayan and Rahim have both been openly critical of the SDPI and the PFI.

The chief minister had last month warned about Right-wing organisations infiltrating peaceful protests against the new citizenship matrix and said that such groups were trying to create law-and-order problems under the garb of protesting against the Citizenship Amendment Act.

Rahim too was threatened. “I am watching every move of yours. You will soon realise who we are. You go and talk against the BJP, not us,” the letter warned, alluding to how Rahim has been attacking the “Popular Front” and the “SDPI”.

“You are nothing for people like us who are trained in (the use of) all kinds of weapons,” the letter added.

Rahim informed a senior police officer who asked him to submit a written complaint. “I complained before the police commissioner who ordered an investigation,” Rahim told The Telegraph on Thursday.

The postmark on the letter bearing a Rs 5 stamp shows it had been posted at a railway station but the exact location appeared smudged.

“I am used to getting such threats and never bothered to lodge complaints. But this time it was about the chief minister and his security. That’s why I approached the police,” Rahim said.

The DYFI acts as the CPM’s youth wing though it identifies itself as an independent organisation.

The PFI, considered a dangerous organisation that imparts arms training to its cadres, was found to have been behind an attack on a professor who is alleged to have set a blasphemous question paper.

Professor T.J. Joseph’s palm was chopped off but was reattached later after several surgeries.

A court had later sentenced 13 PFI cadres to life in prison for the crime.

In Kannur, Kathirur police station has started investigations into the threat letter to Jayarajan, a former secretary of the powerful Kannur district unit and, like the chief minister, a strident critic of communal politics.

Jayarajan found the letter dated February 27 waiting for him at the party office in Kuthuparamba, in Kannur, on Wednesday.

Unlike the handwritten letter that Rahim received, the letter addressed to Jayarajan was printed in English and signed in the name of one Raveendran M.

It even carried the full address of a person by that name in Kannur.

“This letter is about inform(ing) you regarding your punishment date. You are the accused behind the major political crimes and assassinations of Kathiroor Manoj and Shukkur in Kerala. Still you are escaping from the legal actions and punishments. Hence I have decided to give you the final punishment, in memory of all the victims of your brutal crime. You will be murdered soon,” the letter said.

While RSS worker Manoj was murdered in 2017, Indian Union Muslim League worker Shukkur was killed in 2012. Both were victims of tit-for-tat political violence in Kannur in which CPM cadres were arrested.

A police source said the real Raveendran met Jayarajan on Thursday and deposed before the police and claimed his name and address were misused.